Background <p>Promoting mental health through sports participation may be a promising strategy to support the mental health of children and adolescents. This systematic review investigated the perceptions of children and adolescents and of stakeholders close to this target group (e.g., teammates, coaches, parents) on 1) how sports participation influences the mental health of children and adolescents; and 2) factors in sports settings influencing this relationship.</p> Methods <p>A systematic review of qualitative studies was performed. Six electronic databases (CINAHL, PsycInfo, PubMed, Scopus, SPORTDiscus, Web of Science) were searched for relevant studies from inception to 21 August 2024. Out of 1,001 identified records, 25 studies were included. Study quality was assessed using the CASP-tool. Thematic analysis was performed to synthesize findings, which were structured according to the socio-ecological model. Results are presented according to three main topics: 1) mental health outcomes (intrapersonal level of socio-ecological model); 2) individual mechanisms (intrapersonal level); and 3) factors in the sports setting (interpersonal, and organizational and community levels).</p> Results <p>Sports participation influenced various mental health outcomes, including emotions, self-confidence and self-esteem, levels of stress, and resilience, both positively and negatively. Five key individual mechanisms were identified through which sports participation influenced mental health: distraction and focus, performance, personal development, purpose and structure in life, and a sense of belonging. Additionally, interpersonal factors, such as the influence of coaches, teammates and peers, family members, and (team) professionals, appeared important in the relationship between sports participation and mental health. The broader social climate (organizational and community levels) also influenced this relationship. Based on the socio-ecological model and the review findings, a theoretical model was developed illustrating these interconnections.</p> Conclusions <p>The findings confirm the potential mental health benefits of sports participation among children and adolescents, which are largely influenced by interpersonal factors. However, some negative mental health outcomes were also identified and may be underreported. These insights can guide targeted interventions to enhance youth mental health through sports participation, aligned with the proposed theoretical model. Future research should refine this model, assess its applicability across populations, developmental stages, sports activities, and settings, and explore its links with sport drop-out.</p>