Objective: The COVID-19 pandemic has brought unprecedented changes to the lives of youth, including social distancing measures and stay-at-home orders resulting in a sudden and stark reduction in daily social interactions for children and adolescents. Given that peer relationships are especially important during this developmental stage, it is crucial to understand the impact of COVID-19 pandemic on social behavior and risk for mental health problems in children and adolescents. Method: In a longitudinal sample (N=224, aged 7-15 years old) assessed at three strategic time points (prior to the pandemic, during the stay-at-home order period, and again six months later), we examine the social lives of children and adolescents and whether certain social behaviors may protect against increases in internalizing and externalizing problems during the pandemic. Results: Youth who reported lower levels of in-person and digital socialization, greater social isolation, and less peer and parent support had heightened internalizing and externalizing symptoms during the pandemic, controlling for pre-pandemic symptoms. Youth who reported more social connectedness and increased use of digital socialization during the pandemic were less likely to develop psychopathology after experiencing pandemic-related stressors. In addition, children, but not adolescents, who maintained some socialization in-person were less likely to develop internalizing symptoms following exposure to pandemic-related stressors. Conclusion: Using a longitudinal design, we identify social factors that promote well-being and resilience in children and adolescents during this societal event. We provide practical recommendations to mitigate risk of psychopathology resulting from the dramatic changes in youths’ social experiences during the pandemic.