Abstract Background Emerging research suggests that physical activity among children and adolescents decreased during the COVID-19 pandemic. As a summarizing analysis of changes in youth’s physical activity for Europe is lacking, we performed a systematic review and meta-analysis to close this research gap. Amongst others, we examined the relevance of restriction stringency policies and potentially vulnerable groups. Methods In consideration of the PRISMA statement, we searched seven databases and included studies for children and adolescents (≤19 years) of the WHO European Region that compared physical activity during the pandemic with a pre-pandemic baseline using validated measurement instruments. We used the Oxford Stringency Index as an indicator of restriction stringency. Screening for eligibility, data extraction, assessment of the study risk of bias (using ROBINS-E instrument) and certainty grading of evidence (using the GRADE approach), were all done in duplicate. Data were pooled in random effects models (Trial registration: PROSPERO: CRD42023395871). Results Of 14,897 non-duplicate records, 26 publications (n = 15,038 pre-pandemic, n = 13,041 during pandemic) met our inclusion criteria. Comparison before vs during the COVID-19 pandemic revealed a significant reduction in total physical activity (standardized mean difference [SMD], -0.57 [95% CI, -0.95; -0.20]) and moderate-to-vigorous physical activity (SMD, -0.43 [95% CI, -0.75; -0.10]), corresponding to a decrease of 12 min/day (a 20% reduction of the WHO recommendation). Subgroup analyses suggested that children aged 8-12 were particularly affected. The analyses outline a possible association between school closures and more reductions in physical activity. Conclusions A sharp decline in all forms of physical activity was recorded among European children and adolescents during the COVID-19 pandemic, particularly in middle childhood. Policy-makers, teachers and practitioners must act to reverse this decline. Key messages • Physical activity in European children & adolescents decreased significantly during the COVID-19 pandemic. • Immediate action by policy-makers and practitioners is imperative to reverse this trend.