Background: Coronavirus disease 2019 (COVID-19) is different from previous disasters in that it continues to the present and has affected all aspects of family life. During epidemics, psychosocial support is not less important than infection control. During COVID-19-related school closures, prolonged partial closures of schools could have detrimental social and health consequences for children and may increase the burden on the family. Based on a community sample in Korea, this study identified parental concerns, children’s media usage, other various factors and examined whether parental stress level or depression were positively associated with problem behaviors, media exposure, and sleep problems of the primary school children during school closure under COVID-19. Methods: Participants were 217 parents residing in Suwon, South Korea, who had primary school children and responded to a web-based questionnaire on parental concerns from school closure under COVID-19, subjective stress, depression, whether having received mental health services, and family characteristics; children’s sleep patterns, problem behaviors, media usage during the online-only class period, and changes in activity level following the pandemic. Results: During school closure, children gained body weight, spent less time in physical activities and more in media usage. Besides online learning content (97.2%), YouTube was highly used content (87.6%), and games followed (78.3%). Parental subjective stress index was highly associated with parental depression (Pearson correlation 0.439, P< 0.001), children’s sleep problems (0.283, P< 0.001), tablet time (0.171, P= 0.012) and behavior problems (0.413, P< 0.001). Parental depression was associated with children’s sleep problems (0.355, P< 0.001), TV time (0.153, P= 0.024), tablet time (0.159, P= 0.019), and behavior problems (0.524, P< 0.001). Parents who previously received mental services seemed to be more concerned about the problems their children already have getting worse because of COVID-19 than the disease itself. Children’s sleep problem was associated with tablet (0.172, P= 0.011) and smartphone time (0.298, P< 0.001), but not its frequency. Conclusion: During COVID-19-related school closures, many parents and children had various difficulties relating to mental health. Ongoing monitoring of mental health of highrisk groups and multiple support systems may need to be expanded to cover those parents having difficulty in caring for their children.