INTRODUCTION: This systematic review aimed to examine the impact of physical activity-based interventions on body mass index (BMI) reduction in children aged 6-12 years. METHODS: A comprehensive search was conducted in the PubMed database following PRISMA guidelines and using the PICOS framework. A total of 13,927 records were retrieved, of which seven studies met the inclusion criteria. Methodological quality was assessed using the Mixed Methods Appraisal Tool (MMAT). RESULTS: Included studies comprised both preventive and treatment-oriented interventions that aimed to reduce BMI through physical activity. Interventions that integrated family and school components, and were grounded in behavioral theories such as Self-Determination Theory and Social Cognitive Theory, showed greater effectiveness in reducing BMI and improving body composition. DISCUSSION: Multilevel strategies that enhance autonomy, competence, and social support within biopsychosocial frameworks appeared to improve motivation and adherence. Although BMI z-score reductions were modest, they reached clinically meaningful thresholds. These findings support the implementation of context-sensitive, comprehensive strategies involving families, schools, and communities to promote healthy behaviors and sustainable outcomes in pediatric populations. SYSTEMATIC REVIEW REGISTRATION: https://www.crd.york.ac.uk/prospero/, PROSPERO CRD42024547428.