According to the Motorik-Modul-Längsschnittstudie (MoMo, Motor Module Longitudinal Study) of Karlsruhe Institute of Technology (KIT) and Karlsruhe University of Education (PHKA), mental health of children and adolescents decreased during the first lockdown. For children aged between four and 10 years and for girls irrespective of their age, mental health was found to promote physical activity during COVID-induced lockdown in spring 2020. This is reported in Children.