The COVID-19 crisis may have deleterious effects on children's and adolescents' mental health. However, there have been no published studies in which the COVID-related stress symptoms were investigated in a French ordinary pediatric population. The main objective of this study was to examine virus threats and social distancing measures to determine which were more disturbing for children and adolescents, and which were better predictors of post traumatic stress symptoms (PTSS). 1639 parents of children aged between 1 and 18 participated in an online survey. Parents completed questionnaires regarding their children's and adolescents' mental health while in the first French confinement. The data showed that most children and adolescents had PTSS, such as irritability and tantrums, intrusive thoughts or memories, difficulties in falling asleep, aggression, trouble concentrating, and negative emotions. Multiple linear models supported that both virus threats and social distancing- related disturbances were predictors of PTSS scores, with social distancing being a stronger predictor of PTSS scores than virus threats. Additional analyses across age groups revealed that social distancing measures predicted two times more PTSS than virus threat measures in toddlers, while virus threat measures were a stronger predictor of PTSS in adolescents. This is the first study that has investigated stress symptoms in a French pediatric population during the first French confinement episode because of the COVID-19 crisis.