Published reports suggest that the coronavirus disease 2019 (COVID-19) pandemic has had a negative effect on children's mental health (1,2). Emergency departments (EDs) are often the first point of care for children experiencing mental health emergencies, particularly when other services are inaccessible or unavailable (3). During March 29-April 25, 2020, when widespread shelter-in-place orders were in effect, ED visits for persons of all ages declined 42% compared with the same period in 2019; during this time, ED visits for injury and non-COVID-19-related diagnoses decreased, while ED visits for psychosocial factors increased (4). To assess changes in mental health-related ED visits among U.S. children aged <18 years, data from CDC's National Syndromic Surveillance Program (NSSP) from January 1 through October 17, 2020, were compared with those collected during the same period in 2019. During weeks 1-11 (January 1-March 15, 2020), the average reported number of children's mental health-related ED visits overall was higher in 2020 than in 2019, whereas the proportion of children's mental health-related visits was similar. Beginning in week 12 (March 16) the number of mental health-related ED visits among children decreased 43% concurrent with the widespread implementation of COVID-19 mitigation measures; simultaneously, the proportion of mental health-related ED visits increased sharply beginning in mid-March 2020 (week 12) and continued into October (week 42) with increases of 24% among children aged 5-11 years and 31% among adolescents aged 12-17 years, compared with the same period in 2019. The increased proportion of children's mental health-related ED visits during March-October 2020 might be artefactually inflated as a consequence of the substantial decrease in overall ED visits during the same period and variation in the number of EDs reporting to NSSP. However, these findings provide initial insight into children's mental health in the context of the COVID-19 pandemic and highlight the importance of continued monitoring of children's mental health throughout the pandemic, ensuring access to care during public health crises, and improving healthy coping strategies and resiliency among children and families.