The aim of this survey was to investigate the COVID-19 associated restrictions on physical activity (PA) and mental health in youth. A self-assembled questionnaire, including questions on sociodemographic indicators, PA, and mental health, was completed by 188 students (45.7% female, age: 13.97 ± 2.49 years). Data were analysed using Chi-square, and binary logistic regression analysis was used to get a more detailed analysis of influencing factors on mental health, nutrition, and physical activity. For more than one third (36.5 %) of the subjects, mental health deteriorated as a result of the pandemic and the restrictions imposed in connection with it. Worries about the illness of one’s own social contacts (59.0 %), bans on activities (33.0 %) and worries about school or work (33.0 %) were perceived as very stressful. The percentage of children and adolescents meeting WHO activity recommendations decreased from 29.8% before the pandemic to 24.5% during the pandemic. Analogously, the percentage of non-compliance increases from 68.6% before to 73.4% during the pandemic. In each case, 23.9% reported being more or less physically active during the week than before the pandemic. The results emphasize the importance of after-pandemic health promotion strategies and holistic preventive approaches in the school setting.