The COVID-19 pandemic negatively affected child and adolescent mental health, but it is unclear which subgroups were affected most. We investigated to what extent severity and type of mental health problems during and after the pandemic were related to preexisting mental disorders in children in care at child and adolescent mental health services. We employed a repeated cross-sectional design involving data collection at seven time points (April 2020 to April 2023) in a total sample of 2,545…