This systematic review and meta-analysis synthesized evidence of the association between 24-h movement behaviors and social–emotional health and cognitive development in children and adolescents aged 3–18 years from studies using compositional data analysis. Systematic literature searches were conducted on five electronic databases from January 2015 to December 2024. Studies were eligible if they assessed sleep, moderate-to-vigorous intensity physical activity, light intensity physical activity, and sedentary time. Eligible studies also examined associations between movement behaviors and social–emotional health or cognitive development using compositional data analysis in children and adolescents aged 3–18 years. Pooled effect sizes were estimated using cluster robust variance meta-analysis. A total of 19 studies (5 longitudinal, 14 cross-sectional) encompassing 11 826 participants were included. Meta-analysis showed that engaging in more moderate-to-vigorous intensity physical activity, getting more sleep, and spending less time sedentary relative to other movement behaviors was favorably associated with social–emotional health; albeit, the observed relationships were small in magnitude. The association for sleep was stronger among adolescents compared to children. No components of 24-h movement behavior compositions were associated with cognitive development. These findings suggest that engaging in healthy movement behavior compositions may be beneficial for social–emotional health in young people, although the link between 24-h movement behavior compositions and cognitive development is less clear.