Background <p>There are numerous psychosocial and health benefits linked to physical activity; however, 80% of children and youth are not meeting the recommended guidelines. Genetics, socio-economic status and familial factors impact childhood movement behaviors. In particular, active families support well developed and resilient offspring. As the family unit is optimally placed during a critical time in development, it is pertinent to explore the relationship between family functioning and child and youth physical activity. Purpose: To synthesize and analyze the literature to determine the associations between general domains of family functioning (general family functioning, cohesion, communication, conflict, organization, family problem-solving ability, household chaos, and affective environment) and child and youth (children: aged five to 12, youth: aged 13 to 17) physical activity.</p> Methods <p>Literature searches across six databases were performed. Inclusion: Studies that performed and presented a statistical analysis between direct measurements of child and youth physical activity and general domains of family functioning. Exclusion: Indirect measurements of family functioning (e.g., support and encouragement). The summary median effect sizes (Pearson r) and interquartile range [IQR] were calculated between child or youth physical activity and each family functioning domain.</p> Results <p>Search results k = 12,999. Included articles k = 43. Child physical activity had a small median effect size and indeterminate association with general family functioning (<i>r</i> = 0.09; [IQR]: -0.06 to 0.09) and cohesion (<i>r</i> = 0.06; [IQR]: 0.05 to 0.22). Youth physical activity presented with small median effect sizes and significant positive associations with the domains of general family functioning (r = 0.04; [IQR]: 0.02 to 0.06), cohesion (<i>r</i> = 0.09; [IQR]: 0.07 to 0.14), communication (<i>r</i> = 0.17; [IQR]: 0.09 to 0.40), and a negative association with the domain of conflict (<i>r</i> = -0.09; [IQR]: -0.21 to 0.02). Family problem-solving ability, organization, household chaos, and affective environment were understudied across both age groups.</p> Conclusions <p>A small effect size in the domains of cohesion, communication, and conflict highlights the association between child and youth physical activity and family functioning. These findings provide a new avenue for researchers, programmers, and policy writers to target to support child and youth physical activity.</p> Trial Registration <p>This review is registered with The National Institute for Health and Care Research at The International Prospective Register of Systematic Reviews (PROSPERO). PROSPERO ID number is CRD42023454220.</p>