Background: The COVID‑19 pandemic and associated public health measures have disrupted the lives of people around the world. It is already evident that the direct and indirect psychological and social effects of the COVID‑19 pandemic are insidious and affect the mental health of young children and adolescents now and will in the future. The aim and objectives of this knowledge-synthesis study were to identify the impact of the pandemic on children's and adolescent's mental health and to evaluate the effectiveness of different interventions employed during previous and the current pandemic to promote children's and adolescents' mental health. Methodology: We conducted the systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and included experimental randomized and nonrandomized controlled trials, observational studies, and qualitative studies. Results: Of the 5828 articles that we retrieved, 18 articles met the inclusion criteria. We thematically analyzed them and put the major findings under the thematic areas of impact of the pandemic on children's and adolescents' mental health. These studies reported that pandemics cause stress, worry, helplessness, and social and risky behavioral problems among children and adolescents (e.g., substance abuse, suicide, relationship problems, academic issues, and absenteeism from work). Interventions such as art-based programs, support services, and clinician-led mental health and psychosocial services effectively decrease mental health issues among children and adolescents. Conclusion: Children and adolescents are more likely to experience high rates of depression and anxiety during and after a pandemic. It is critical that future researchers explore effective mental health strategies that are tailored to the needs of children and adolescents. Explorations of effective channels regarding the development and delivery of evidenced-based, age-appropriate services are vital to lessen the effects and improve long-term capacities for mental health services for children and adolescents. Key Practitioner Message: The COVID-19 pandemic's physical restrictions and social distancing measures have affected each and every domain of life. Although the number of children and adolescents affected by the disease is small, the disease and the containment measures such as social distancing, school closure, and isolation have negatively impacted the mental health and well-being of children and adolescents. The impact of COVID-19 on the mental health of children and adolescents is of great concern. Anxiety, depression, disturbances in sleep and appetite, as well as impairment in social interactions are the most common presentations. It has been indicated that compared to adults, this pandemic may continue to have increased long term adverse consequences on children's and adolescents' mental health. As the pandemic continues, it is important to monitor the impact on children's and adolescents' mental health status and how to help them to improve their mental health outcomes in the time of the current or future pandemics.
Keywords: COVID-19; adolescents; children; epidemic; mental health; pandemic.