Résumé : Background and Objectives: The COVID-19 pandemic and its associated factors have been shown to affect anxiety levels of young people. We meta-analytically assessed the prevalence of anxiety symptoms and anxiety disorders in children and adolescents during the pandemic, and the predictors and moderating factors influencing anxiety. Methods: Multiple databases and registers were searched in this PRISMA and MOOSE-compliant systematic review and meta-analysis (PROSPERO:CRD42021266695) until 27/06/2021. We included individual studies evaluating the prevalence and characteristics of anxiety symptoms or anxiety disorders in children and adolescents (mean age ≤18 years), during the COVID-19 pandemic. Data extraction and quality assessment were carried out by independent authors. Random-effects meta-analyses of the prevalence of anxiety symptoms and anxiety disorders were conducted using Comprehensive Meta-Analysis (CMA) V3. Results: 74 articles (total participant sample=478,882) were included (mean age=13.4 years, 52.3% female). The pooled rate of children and adolescents fulfilling diagnostic criteria for anxiety disorders was 13.0% (95%CI=4.9–30.1); the pooled prevalence of anxiety symptoms was 26.5% (95%CI=20.3–33.9). Anxiety symptoms were significantly more prevalent in females than males (B = 0.103, p<.001), significantly higher during the second wave of COVID-19, following July 2020, than during the first wave, prior to June 2020, (Q= 8.136, p=.017), and during school closure (Q= 8.100, p=.014). Quality of included studies was overall moderate. Conclusions: There is a high prevalence of anxiety symptoms in children and adolescents during the COVID-19 pandemic, especially amongst females. This study identifies vulnerable groups, risk, and protective factors, which is crucial to developing clinical practice to prevent further mental health deterioration in young people.