Background: The COVID-19 pandemic has posed an unprecedented threat to global mental health. Children and adolescents may be more susceptible to mental health impacts related to their vulnerable developmental stage, fear of infection, home confinement, suspension of regular school and extracurricular activities, physical distancing mandates, and larger scale threats such as global financial recessions and associated impacts. Our objective was to review existing evidence of the COVID-19 pandemic's global impact on the mental health of children and adolescents <19 years of age and to identify personal and contextual factors that may enhance risk or confer protection in relation to mental health outcomes. Methods: We conducted a search of peerreviewed and preprint research published in English from January 1, 2020, to February 22, 2021. We included studies collecting primary data on COVID-19-related mental health impacts on children and adolescents. We graded the strength of included articles using the Oxford Centre for Evidence-Based Medicine rating scheme. Results: Our search and review yielded 116 articles presenting data on a total of 127,923 children and adolescents; 50,984 child and adolescent proxy reports (e.g., parents, healthcare practitioners); and >3,000 chart reviews. A high prevalence of COVID-19-related fear was noted among children and adolescents, as well as more depressive and anxious symptoms compared with prepandemic estimates. Older adolescents, girls, and children and adolescents living with neurodiversities and/or chronic physical conditions were more likely to experience negative mental health outcomes. Many studies reported mental health deterioration among children and adolescents due to COVID-19 pandemic control measures. Physical exercise, access to entertainment, positive familial relationships, and social support were associated with better mental health outcomes. Conclusions: This review highlights the urgent need for practitioners and policymakers to attend to and collaborate with children and adolescents, especially those in higher risk subgroups, to mitigate short-and long-term pandemic-associated mental health effects. Key Practitioner Message• Children and adolescents are at crucial phases of development, making them more susceptible to negative mental health impacts of the COVID-19 pandemic and response measures.• In this review, children and adolescents were found to experience more depressive and anxious symptoms than reported prepandemic rates, specifically with high levels of fear and concern regarding the impact of COVID-19 on their lives.• Factors associated with worse COVID-19 mental health outcomes were older adolescent age, female gender, neurodiversity, and the presence of chronic physical conditions.• While this review captures emerging data, study designs that utilize validated measures and undertake longitudinal data capture will greatly improve understanding of impacts.• Pandemic-associated negative impacts on child and adolescent mental health are clear and must be...