Participation of Children and Youth in Mental Health Policymaking: A Scoping Review [Part I]

Although youth participation is oft-acknowledged as underpinning mental health policy and service reform, little robust evidence exists about the participation of children and youth in mental health policymaking. A scoping review based on Arksey and O’Malley’s framework was conducted to identify and synthesize available information on children and youth’s participation in mental health policymaking. Published studies up to November 30, 2020 were searched in Medline (OVID), PsycINFO (OVID), Scopus, and Applied Social Sciences Index and Abstracts (PROQUEST). Further studies were identified through Google Scholar and a grey literature search was conducted using Google and targeted web searches from October to December, 2020. Three reviewers performed screening and data extraction relevant to the review objective, followed by an online consultation. From 2,981 records, 25 publications were included. A lack of diversity among the youth involved was found. Youth were often involved in situational analysis and policy design, but seldom in policy implementation and evaluation. Both the facilitators of and barriers to participation were multifaceted and interconnected. Despite a range of expected outcomes of participation for youth, adults, organizations, and communities, perceived and actual effects were neither substantially explored nor reported. Our recommendations for mental health policymaking highlight the inclusion of children and youth from diverse groups, and the creation of relational spaces that ensure safety, inclusiveness, and diversity. Identified future research directions are: the outcomes of youth participation in mental health policymaking, the role of adults, and more generally, how the mental health of children and youth shapes and is shaped by the policymaking process.


Background
Youth mental health is a growing priority in the global health agenda. Indeed, there is growing recognition that investing in children's and youth's mental health is crucial to their wellbeing and their ability to actively participate in society now and as adults (Rose et al., 2017). Three quarters of all mental health challenges start by the mid-20 s (Kessler et al., 2007) and about 10-20 % of children and adolescents worldwide experience diagnosed mental health conditions (Kieling et al., 2011).
The participation of children and youth in service delivery planning, research, and policymaking has been shown to improve the mental and physical health outcomes of the children and youth who participate (Jenkins et al., 2018;CYCC Network, 2013;Oliver et al., 2006;Price & Feely, 2017). Moreover, participation provides youth with a sense of power and control of their own identity (Ungar & Teram, 2000). The involvement of children and youth in decisionmaking is enshrined in Article 12 of the Convention on the Rights of the Child (UNGA, 1989). It stipulates that children (i.e., people under the age of 18 years) have the right to express their views freely in all matters that affect them. This includes judicial and administrative proceedings and policymaking processes at all levels of government. Public participation rights have also been recognized for individuals 18 years of age and older in other treaties such as the International Covenant on Civil and Political Rights (UNGA, 1966), which highlights the crucial role that people play in promoting governance through equal access to public services (Art. 25).
Initiatives to engage children and youth in mental health policy are gaining momentum, notably in Australia, Canada, and the United Kingdom (UK) (Government of Canada, 2018Orygen, 2020;United Nations, 2010;Young Minds, 2017). These initiatives are aligned with a positive youth development approach that views children and youth as active contributors to their own development and to their communities (Iwasaki, 2016). Yet, participation of children and youth is seen more often in service planning, implementation, evaluation, and research than in policymaking (Jenkins et al., 2020a(Jenkins et al., , 2020b. On the other hand, little is known about what has been done to facilitate the consistent and meaningful inclusion of children and youth as actors/agents in policymaking in the field of mental health (Jenkins et al., 2020a(Jenkins et al., , 2020b. Indeed, some marginalized groups-such as teenage parents, youth living or spending time on the street, racialized, unemployed, and Indigenous children and youth, and those in the criminal-legal system-are often left out of decisions that affect their lives (Mohajer & Earnest, 2010). At the same time, a range of social determinants such as gender, poverty, and racism disproportionately affect mental health of these marginalized groups.
In this context, a scoping review of publications describing the current state of child and youth participation in mental health policymaking is needed to guide and sustain future research and decision-making in this field. In our review, policymaking is broadly defined in a spectrum where participation can be found at different stages of a policy cycle, including research participation and dissemination of knowledge aiming to inform policies (Macauley et al., 2022;OECD, 2017).

Method
We conducted this scoping review in accordance with established frameworks and methodology guides (Arksey & O'Malley, 2005;Peters et al., 2020aPeters et al., , 2020b. The review was structured in six stages: (1) defining the review question; (2) identifying relevant studies and searching the academic and grey literature; (3) selecting relevant studies; (4) extracting data relevant to research questions; (5) analyzing and reporting data that respond to the review questions; and (6) conducting stakeholder consultations with children and youth, policymakers, and adult facilitators of child and youth participation. A preliminary search of PROSPERO, MED-LINE, the Campbell Collaboration Library, the Cochrane Database of Systematic Reviews, and the Joanna Briggs Institute Database of Systematic Reviews and Implementation Reports was conducted and no existing or underway scoping reviews or systematic reviews on the topic were identified. The scoping review protocol was registered in Open Science Framework (OSF) on November 30, 2020 (https:// doi. org/ 10. 17605/ OSF. IO/ H5ERX).

Identifying the Review Question
The main review question, developed after considering the purpose of the review (Arksey & O'Malley, 2005), was: What information is available on child and youth participation in mental health policymaking? We subsequently came up with the following sub-questions: (1) What are the socio-demographic characteristics of the children and youth participating in mental health policymaking? (2) In what geographical and substantive contexts have children and youth participated in policymaking? (3) What is the extent and nature of child and youth participation? (4) What facilitators of, barriers to, and effects (expected or documented, individual or collective) of the participation of child and youth in mental health policymaking have been reported?

Inclusion and Exclusion Criteria
We included literature examining the participation of children and youth in mental health policymaking. Children under the age of 18 years according to the United Nations Convention on the Rights of the Child (UNGA, 1989) and youth between 15 and 24 years of age according to the United Nations definitions of youth (UNDESA, n/d) were considered. Other common terms (i.e., child, adolescent, youth, young adults, and emerging adults) were used in the literature search. The search strategy is included in Appendix I (Supplementary Material).
In terms of content, we included sources that explored the active participation of children or youth in mental health policymaking or evaluated interventions to support child and/or youth participation in mental health policymaking. Participation in policymaking can range along a continuum of levels and take place at different points in the policymaking process. A broad definition of policymaking was thus applied; both formal and informal participation processes where youth are engaged in information sharing, consulting (e.g., public meeting, youth council), or collaborating (e.g., youth advisory group, participatory research) to directly or indirectly influence policy agenda, directions or decisions within a policy cycle in government, school, and community settings. We included studies that: took place in any geographic location (i.e., including high-, middle-, and lowincome countries); involved any subgroup of the population; and pertained to any type of public mental health policy, any phase of the policymaking process, and level of government. We included a comprehensive definition of mental health policymaking, encompassing a range of interventions, from 1 3 the promotion of wellbeing to the prevention of mental illnesses (Stewart-Brown, 2017;Weijers & Jarden, 2017).
In this scoping review, we considered published primary sources of evidence and grey literature and reviews if they included not only an evidence synthesis but also consultations. Studies could be of any type of design (i.e., quantitative, qualitative, and mixed methods), policy documents, agency reports, etc., available in English. In order to minimize the risk of omitting relevant sources, no specific criteria were applied for heterogeneous types of data presented in retained publications. We excluded documents focusing on policymaking that were not related to mental health or that addressed adults only or that addressed the entire general population, without any specific focus on children and youth. Also, bibliometric analyses, book chapters, reviews that did not include consultations, protocols, conference/seminar proceedings, editorials, letters to the editor, and introductions to issues and special issues were excluded.

Search Strategy
A research librarian conducted the main search using key/ text words and subject headings identified from existing knowledge and the titles, abstracts, and index terms of relevant articles on the topic based on the results of an initial limited search in Medline (Online Appendix 1). This search strategy was independently validated by another research librarian. Four bibliographic databases were searched on November 30, 2020: Medline (OVID interface), PsycINFO (OVID interface), Scopus, and Applied Social Sciences Index and Abstracts (PROQUEST interface). We did not apply any date or language restrictions. The grey literature was searched in English through Google Advanced Search for published materials that met the inclusion criteria between October and December 2020. The keywords used to search for grey literature include: child; children; youth; adolescents; young adults; emerging adults; mental health; mental illness; mental disorder; wellness; well(-) being; ill(-)being; mental health policy; mental health policy development; mental health policy making; policy making; policy development; participation; inclusion; engagement; consultation; co-creation; co-production; co-design; decision-making; shared decision-making; input; experiential; advocacy; well(-)being promotion; mental illness prevention; and, mental health promotion. We further identified other sources through team members' existing networks of researchers and relevant organizations working in the field globally. Relevant grey literature sources were identified by examining the context, precision, and quality of key concepts used in the references and how these potentially related to the research questions.

Source of Evidence Selection
All identified records (n = 2,981) were merged into EndNote X9 (Clarivate Analytics, PA, USA) and duplicates (n = 514) were removed (Fig. 1). Three independent reviewers (AH, PM, SY) conducted a pilot screening of titles and abstracts of 20 records (randomly selected) against the inclusion criteria for the review and continued the same process until 80% interrater reliability was established. Then, these three independent reviewers assessed the full text of the potentially relevant records against the inclusion criteria. Disagreements at any stage were resolved through discussion or by a senior team member.

Data Extraction/Charting
The data were extracted from 25 sources retained by three independent reviewers (AH, PM, SY) into an Excel spreadsheet. By adapting the JBI template source of evidence details, characteristics and results extraction instrument (Peters et al., 2020a), we extracted general information about the source as well as specific details about the participating population, study design, and key findings relevant to the review objectives. Due to a range of retained publications, three reviewers met after the initial charting process and becoming familiar with the study data in order to ensure consistency of the data that each reviewer was extracting with review questions. Disagreements at any stage were resolved through discussion or by an independent researcher (NB, MRC). We did not conduct a quality assessment of retained

Fig. 1
Search results and article selection and inclusion process. Flow Diagram for the scoping review process adapted from the PRISMA statement by Moher and colleagues (2009) 1 3 studies following the principles of scoping review methodology (Arksey & O'Malley, 2005).

Consultation
We conducted online individual and group interviews to validate the findings, inform future research, and develop knowledge dissemination strategies (Arksey & O'Malley, 2005;Levac et al., 2010). 44 participants with direct experience in policy processes in mental health were recruited from 16 countries in three categories: (a) youth aged 14-24 years, (b) policymakers, and (c) adult facilitators of child and youth participation in mental health policymaking. Preliminary review findings were shared with participants and they were then invited to comment on them and identify what was missing from the findings (Hawke et al., 2019). The findings of these consultations are presented in a separate publication [Part II] of the current series.

General Information About Evidence Sources
As shown in Fig. 1, a total of 2,981 publications were identified from the database and manual search, and 25 publications were retained for full extraction. As shown in Table 1, these included 11 peer-reviewed studies, 10 agency reports, three policy documents, and one doctorate thesis. Nineteen employed qualitative methods, while one used mixed methods. Nine publications had an objective of directly influencing youth mental health policymakers through child and youth participation. Other objectives included: better understanding of child and youth perspectives and experiences; advancing participatory research/models; synthesizing evidence/current programs; and evaluating child and youth engagement and participation strategies and mechanisms.

Socio-Demographic Characteristics of Participating Children and Youth
Whenever the ages of child and youth participants were specified in the publications (n = 15), they fell between 10 and 26 years. Eleven publications clearly stated the ethnicity of children and youth participants, including Indigenous (n = 6), Pacific Islanders (n = 4), African American and/or Latino (n = 3), and Asian (n = 3) people. The World Economic Forum and Orygen (2020) also reported participation of children and youth from 50 countries from all six inhabited continents. Eight publications reported the gender-ratio among children and youth participants, which ranged from more women (n = 5), equal women and men (n = 1), and more men (n = 2). Among three publications that reported on the sexual orientation of participants, non-binary youth participation ranged from 1.9% to 3.0%. While socio-economic status (SES) of participants was similarly not mentioned in 18 retained publications, the rest (n = 7) reported inclusion of participants with low or low-to-middle SES. The lived experiences of mental illness among children and youth participants, as reported in 14 publications, included those of mental health problems in general (n = 11), substance use (n = 2), psychosis (n = 1), and depression (n = 1). In addition, one publication described a small number of youth participants going through grief and loss issues due to suicide by close friend or family member. Educational attainment and disabilities of participants, which were not initially considered for extraction, were later extracted based on input from the consultations. Among the seven publications that reported the educational attainment of youth participants, the majority of participants in four publications were enrolled at schools (middle school, high school, university, etc.), and three publications also included child and youth participants who were not in formal education or had trouble at school. Only three publications reported that children and youth with unspecified disabilities participated, with the proportion of those with disabilities among total participants ranging from 6%  to 24% (Research and Training Center on Family Support and Children's Mental Health, 2009).

Contexts of Child and Youth Participation: Policy Type, Content, and Scope
The retained publications focused on different types of policies/instruments. Six publications focused on mental health (Australian Infant Child Adolescent and Family Mental Health Association, 2008;Braddick, Carral, Jenkins, & Jané-Llopis, 2009;Mental Health Commission of Canada, 2015; Research and Training Center on Family Support and Children 's Mental Health, 2009;Rodarmel, 2013;Simmons et al., 2020), four on youth health more broadly (New Zealand Ministry of Health, 2002;Ott et al., 2011;Percy-Smith, 2007;Sheridan et al., 2014), and one on youth policy broadly (Victoria State Government, 2016). Other types of policies included frameworks, guidance manuals/toolkits/ guides, acts, and a sustainable development agenda. Nineteen publications had a general focus on mental health, and two focused on both physical and mental health (New Zealand Ministry of Health, 2002; Sheridan et al., 2014). Other specific foci were on stress (n = 3) Percy-Smith, 2007;Soleimanpour, Brindis, Geierstanger, Kandawalla, & Kurlaender, 2008) and psychosis (n = 1) (Jones, 2015). Indigenous holistic perspectives of health were considered in three publications (Aboriginal Life in Vancouver Enhancement Society, 2020; Mental Health Commission of Canada, 2015; New Zealand Ministry of Health, 2002); and two publications, focused on general youth policies, also considered housing and employment (Aboriginal Life in Vancouver Enhancement Society, 2020; Victoria State Government, 2016). While the scope of two publications was at the global level, 12 publications had a national scope, which was limited to Canada, Australia, New Zealand, US, UK, Vanuatu, and 15 European countries. Additionally, seven publications described work at the state/provincial level, and four publications focused on municipal/county-level policies.

Roles of Children and Youth Participants
As shown in Table 2, children and youth played different roles in mental health policymaking, including: (a) informants who provided feedback on mental health frameworks, policies, and services (n = 14); (b) co-creators with adults in the design of mental health services, policies, and tangible products (e.g., leaflets and websites) (n = 12); (c) advocates who disseminated their perspectives and knowledge to the general public, researchers, and policymakers in collaboration with organizations (n = 11); and (d) co-researchers who were often involved in participatory research (n = 7). They were provided training in research methods (Percy-Smith, 2007;Simmons et al., 2020;Soleimanpour et al., 2008), and were involved in adapting the data collection tools to be youth-friendly Rodarmel, 2013), conducting surveys Soleimanpour et al., 2008) and analysis , supporting their peers (Jones, 2015;Simmons et al., 2020), and training staff (Young Minds 2017).

Roles of Adult Participants
Adults also played different roles in mental health policymaking along with children and youth, including (a) informants who provided their views and feedback (n = 12); (b) trainers who helped children and youth participants develop a variety of skills such as communication skills and youth mental health first aid (n = 8); (c) supervisors who oversaw the implementation of projects (n = 6); (d) mentors (n = 4); (e) coordinators (n = 3); (f) experts who recommended actions from a process of discussion, debate, and feedback (n = 3); and (g) co-chairs who sat together with youth in a working group (n = 2) although the balances of power between children and youth and adults in group processes and decision-making varied.

Purpose and Methods of Child and Youth Participation
When the primary purpose of child and youth participation was to identify a policy gap, they were consulted through focus groups (n = 2) Sheridan et al., 2014), surveys (n = 4) Rodarmel, 2013;Soleimanpour et al., 2008;Young Minds, 2017), and interviews (n = 1) (National Mental Health Commission of Australia, 2017). In particular, visual material such as videos and posters, was identified as an effective communication method for children and young people, to share their key health issues in their daily lives (Percy-Smith, 2007). When children and youth were consulted about the content of policy and frameworks, they were consulted through interviews (n = 1) (World Economic Forum & Orygen, 2020) Government, 2016;World Economic Forum & Orygen, 2020). In addition, children and youth often joined working groups such as a Youth Reference Group and a Youth Council, to participate in iterative brainstorming, feedback, and reflection processes.
For the purpose of advocacy, children and youth shared their perspectives and experiences at various public forums

Policy Stage of Child and Youth Participation
The forms and levels of participation of children and youth can differ depending on the stages of the policy cycle: (i) analysis of the situation; (ii) policy design and planning; (iii) implementation; (iv) monitoring and evaluation; (v) and advocacy and participatory debate that feeds back into ongoing situation analysis (OECD, 2017). As Table 1 shows, child and youth participation was part of situation      Government, 2016). No retained publications found child and youth participation at the implementation stage. In Garcia et al. (2014), despite the successful policy change through youth's participation and advocacy work, policy implementation faced challenges due to the complex political environment and the local realities of poverty, homelessness, and criminalization in Skid Row, Los Angeles. One publication reported youth participation in evaluation. Bourke and MacDonald (2018) conducted an evaluation of a school-based mental health program across Aotearoa New Zealand. The evaluation results were disseminated to policymakers. The participation of children and youth at the stage of advocacy and participatory debate was found in seven publications. For instance, the Youth Alliance played a key role as the 'public face' in over 35 community awareness activities, presentations, and workshops in the Central Coast region of New South Wales, Australia .

Duration of Youth Participation
Youth participation ranged in duration from less than a year (

Facilitators of Child and Youth Participation
Factors identified as facilitators of child and youth participation (accessibility, flexibility, practical support, training, safe environment, personal belief, accountability) appeared multifaceted and interconnected at different levels (individual, microsystem, mesosystem, macrosystem, and socio-political landscapes) when mapped onto an adaptation of the ecological model of participation of children and youth proposed by Gal (2017) (Table 3 (2007) their own capacity and commitment (n = 2); accessibility related to the internet/online platform (n = 6) and transportation (n = 2); and financial compensation (monetary or a voucher) or reimbursement (n = 5). A flexible schedule was key for children and youth with competing interests such as school or part-time work, and flexibility also meant accommodations when mental health conditions fluctuated (n = 4). At the mesosystem level, one major facilitator was practical support, including clear communication and mentoring/ coaching from adult participants (n = 9); administrative support (n = 3); and peer support (n = 3). In addition, a school credit system, which recognizes the participation of child and youth, was seen as particularly important to engage those at risk or who were tenuously engaged within their school setting (Australian Infant Child Adolescent and Family Mental Health Association, 2008). Furthermore, youth were encouraged and motivated by training for skills development as this could add value to their CVs (n = 7). Another major facilitator within the mesosystem was a safe environment characterized by cultural safety (n = 2); equitable decision-making (n = 5); diversity to support minority group participation (n = 3) and inclusiveness (n = 3); confidentiality (n = 1); and appropriate accountability through feedback to child and youth participants (n = 2). The media also played a role in promoting opportunities, updates, and outcomes of programs and initiatives (n = 2).

Barriers to Child and Youth Participation
Barriers to child and youth participation also mapped onto different levels of the ecological model (Table 3). At an individual level, their availability was impacted by their lack of belief/confidence in the process of change (n = 3), their lack of time due to their multiple responsibilities and competing interests (n = 9), and the fluctuation of their mental health status (n = 4). Limited access to the internet and difficulty finding helpful information regarding opportunities and organizations to get involved in were seen as limiting participation (n = 3). At the level of the microsystem where parents and families are involved, parents'/guardians' disapproval of participation in activities can limit child and youth participation (n = 1).
At the level of the mesosystem where children and youth interact with adults, identified barriers were: lack of flexibility in planned activities and/or organizational structures that did not address the changing needs of youth (n = 4); and lack of practical support, including lack of financial compensation (n = 7), accommodation for special needs (n = 4), support and action from adults (n = 4), and training children and youth on research skills (n = 1).
Relational space with adults/peer youth participants affected youth participation. Lack of power sharing with adults (n = 10) and "tokenism" (n = 4) were often mentioned as barriers to participation. In addition, lack of diversity and discrimination could result in limiting participation of certain groups of children and youth such as those with communication difficulties, disabilities, behavioural problems, cultural barriers, younger children, youth no longer engaged in the educational systems, those from traveller communities (e.g., Roma Slovak), rural areas and low-SES backgrounds, and child and youth carers and/or parents (n = 3). Despite the adults' effort to increase diversity, when participants from diverse backgrounds (e.g., class, SES) worked together, group dynamics could be a challenge as those from lowerincome families did not necessarily feel comfortable interacting with those from high-income families (n = 3).
Furthermore, lack of accountability and lack of clear communication of expected roles were identified as barriers to participation (n = 2). More broadly, lack of media attention (n = 2) and lack of political will/interest can undermine motivation to participate (n = 2).

Youth: Expected and Perceived/Actual Outcomes
Fifteen publications mentioned that children and youth were expected to increase their sense of empowerment, self-efficacy, and control over their decisions as a result of their participation in policymaking processes (Table 4). Other expected outcomes in relation to policymaking found in the retained publications were: improved physical/mental health outcomes and wellbeing (n = 8); personal growth and skills development (n = 6); better access to more youth-informed and youth friendly mental health services and programs (n = 4); increased sense of community (n = 3); and increased participation in the workforce (n = 2); and reduced internalized stigma (n = 1).
The perceived/actual effects of participation on children and youth have not been fully explored or reported (n = 10). Among the reported perceived/actual effects of child and youth participation in mental health policies and programs for the child and youth participants were: the prevention of mental health problems (n = 13); having youth voice/needs being heard through dialogue (n = 10); positive feelings such as feelings of making progress, engagement, self-confidence, and inclusion (n = 6); and skills development and the fostering of professional aspirations (n = 4).

Adults: Expected and Perceived/Actual Outcomes
The reported expected outcomes for adults were: better understanding of child and youth perspectives and needs (n = 6); and adults being empowered in seeing youth's Table 4 Individual and collective outcomes of child and youth participation Level Expected outcomes Table 4 (continued)    (2017) Reduce stigma Davidson et al. (2010), Jones (2015), Young Minds (2017) Raise public awareness Mental Health Commission of Canada (2015), Orygen and World Economic Forum (2020) confidence in their competence and potential for change (n = 3). As was the case for children and youth, 14 publications did not mention actual/perceived benefits for adults. The reported actual/perceived benefits for adults included: adults learning about new and diverse perspectives and experiences of children and youth (n = 4); finding the gap between policies and practices (n = 3); and feeling empowered and inspired (n = 3).

Organizations: Expected and Perceived/Actual Outcomes
Improved mental health services was the most mentioned expected outcome for organizations (n = 15). Other expected outcomes were: the transformation of organizations into youth-focused agencies (n = 8); the development of a youth engagement model (n = 2); and better understanding of the impact of implemented programs through youth participation (n = 1).
Fourteen publications did not mention actual/perceived effects of children and youth participation at an organizational level. Four publications reported that organizations became sites of sustainable youth engagement, while three reported organizational contributions to improving youth mental programs/services. Other stated outcomes included: strengthened youth-adult relationships (n = 3); improved quality of staff/overall organizational work (n = 3); and increasing networks (n = 3).

Communities: Expected and Perceived/Actual Outcomes
For this review, we broadly defined "community" as different environments/levels of society, to capture the effect of programs, policies, and associated changes on local, national, and/or international environments. The often-cited expected outcomes of youth participation are: more locally/culturally relevant and accessible mental health services and policies (n = 18), and healthier and stronger communities (n = 14). Participation of children and youth, particularly those who are marginalized and disenfranchised in a community, was expected to generate a sense of community, connectedness, inclusion, and cohesiveness (n = 7), and also reduce stigma (n = 3). Child and youth participation in policy development was expected to narrow policy-practice gaps in the field of mental health (n = 5) and raise public awareness (n = 2). Ten publications stated that child and youth needs and perspectives were identified for future policy/service development. Other outcomes included: the development of models, frameworks, or councils for youth-friendly policies and services (n = 5); youth-oriented policies (n = 5); and strengthening of youth-serving sectors by fostering existing and new networks with partner organizations (n = 4). Garcia et al. (2014) also reported that a community-based participatory research process strengthened social cohesion and created neighborhood wellness.

Consultation
Consultation, though being an optional stage of a scoping review, added methodological rigor to the current study (Levac et al., 2010). Consultation participants found the preliminary findings largely consistent with their own experiences and provided additional insights. We used their feedback to revisit some aspects of the preliminary findings and refine the analysis. In addition, the shared experiences and perspectives helped contextualize the review findings and identify research gaps in the existing literature. Findings from our consultation are presented in a separate publication [Part II].

Who is and Who is not Participating in Mental Health Policymaking?
The representation of young people with diverse backgrounds in terms of ethnicity, gender, SES, educational attainment, and disabilities was limited in the retained publications. In addition, only 56% of the retained publications explicitly stated involvement of people with living and lived experience in policymaking, while it is often unclear what counts as living and lived experience of mental illness (diagnosis versus subjective experience versus family members with mental illnesses). Ethnicity (n = 11), gender (n = 14), SES (n = 16), and lived experiences (n = 10) were "unspecified/unknown" in the retained publications. Since various adverse experiences, such as gender discrimination, racism, and poverty, affect mental health (Reiss, 2013;Vines et al., 2017;Wilson et al., 2016), it is important to clarify what kind of experiences and perspectives are represented in policymaking processes.
The reviewed publications were mainly concentrated in Canada, Australia, New Zealand, UK, and US. There is thus a dearth of understanding about how the Western concept of "child participation" as a rights-based approach is implemented in low-and middle-income countries (LMICs), and how cultural values related to gender and family customs and socio-economic conditions of everyday life shape the way children and youth partake in mental health policymaking (Faedi Duramy, 2015;Faedi Duramy & Gal, 2020;Wyness, 2012).

How are Children and Youth Participating?
The roles of children and youth and their level of participation are closely linked with the purpose and methods of participation as well as roles of adults. The role played by adults had bearing on the extent to which participation of young people as informants was passive versus involving more active collaborative roles such as "co-creators". The perspectives of young people presented in a few retained publications Mental Health Commission of Canada, 2015) suggest that adults support children by providing guidance and assisting for their skills development, while ensuring child and youth participants could maintain the autonomy they desired. Furthermore, children and youth may have had negative experiences in the mental health system or have mistrust and feelings of discomfort around adults. It is noteworthy that how trust was built and how levels of influence and interdependence in adult-child relationships were negotiated and rebalanced in the whole participation process remain largely unexplored.
While two-to-three years of engagement was often found among the retained publications, temporal elements of policymaking processes (one-off, continuous, irregular, regular) can affect the extent to and the forms in which young people participate in decision-making processes (Gal, 2017;Tisdall, 2015). This temporal aspect of child and youth participation is also important to consider as it is related to the policy stage of participation. In this review, retained publications found child and youth participation in the stages of situational analysis, policy design and planning, and advocacy, yet none in the stage of policy implementation. To what extent child and youth participation leads to policy change that has an impact on their mental health remains unanswered as well. Different temporal elements should be further explored for the meaningful and sustained participation of children and youth in policymaking processes.

What Facilitates and Hinders Child and Youth Participation?
The mental health of child and youth participants emerged as a factor closely related to several facilitators and barriers. While flexibility to accommodate individual mental health needs can be a facilitator of participation, fluctuating mental health levels and/or inadequate attention to these or associated needs can limit child and youth participation (Jones, 2015). In addition, lack of financial compensation can affect participants' mental health as financial health influences mental health . Furthermore empirical understandings of the dynamic ways in which the mental health of children and youth can affect as well as be affected by the process of their participation in policymaking, directly and indirectly, will provide practical insights into how to create safe and engaging spaces for child and youth participants with mental illness.
While various barriers and facilitators are interlinked at different system levels in an ecological model of child and youth participation, only one barrier at a family level, permission from guardian/parent, and one family level-facilitator, a family council, were reported in one publication each. This may indicate less attention being paid to the role of family in promoting or hindering child and youth participation (Muddiman et al., 2019). Attention to potential positive and negative factors in the family environment that can support child and youth participation; and facilitate their access to services, confidentiality, and privacy is also warranted.

What are the Effects of Youth Participation?
The effects of child and youth participation are widely reported not only for children and youth but also for adults, organizations, and communities. However, there was a lack of evidence to know if aspired-to effects were or were not met, such as the extent to which participation can be therapeutic and lead to a long-term positive impact on participants' mental health and living conditions. Expected and perceived/actual effects for adults were also largely unreported. While adults may take on the role of "audience", who listen to the views of young people to influence policy and daily life practices (Lundy, 2007), child and youth participation processes involve relational experiences that are shaped by the power dynamics between young people and adults who have respective roles and positions (Wyness, 2012). Considering the interdependent relations between young people and adults (Wyness, 2012) and the evolving nature of children and youth's participation processes, an evaluation of multiple dimensional effects of their participation at different levels (young people, adults, organizations, and communities) is warranted to meet the changing needs and interests of children, youth, and other stakeholders .

Limitations
Some relevant publications may not have been retrieved by our search strategy due to the broadness and complexity of concepts of participation, mental health (e.g., spiritual health) and policy. Despite the inclusion of grey literature, many relevant initiatives seem to be happening only on the ground and not reflected in websites or publications, or are not described in English or French. On the other hand, a range of information presented in diverse types of publications made characterization and interpretation of the retained publications challenging and be subject to reviewer bias. In addition, generalizability may be limited due to lack of quality assessment of each publication. Although our extraction framework incorporated the perspectives of all team members, another limitation is that it was largely based on the perspectives of adult researchers. To address this limitation, we had adult researchers with extensive experience of participatory research involving children and youth as well as youth and young adult students in our team.

Conclusion
Our review highlights concrete recommendations for mental health policymaking around the inclusion of children and youth from diverse groups, and the creation of relational spaces that ensure safety, inclusiveness, and diversity. It also identifies future research directions such as the outcomes of youth participation in mental health policymaking, the role of adults, and more generally, how the mental health of children and youth shapes and is shaped by the policymaking process.