Pandemics such as the COVID-19 pandemic can cause stress and psychopathological symptoms, particularly in parents and families. To date, few studies have examined post-traumatic stress symptoms (PTSS) before and during the pandemic in parents and related risk factors as well as associations with children’s psychological symptoms. Therefore, in this cross-sectional online study parents (N = 670, 90% female, M = 38.5, SD = 6.5) were asked about their own psychopathological symptoms (anxiety, depression, PTSS; current and retrospective) and their children’s psychological symptoms. Results showed that parents report most strongly PTSS symptoms during the pandemic compared to pre-pandemic retrospective recall (d = 0.84; anxiety and depression d ≤ 0.63), with parents observing emotional symptoms in their children in particular (d = 0.46, other domains d ≤ 31). While 11.8% of parents reported elevated scores for PTSS before the pandemic, 22.7% did so during the pandemic. Between child and parental psychopathology, the strongest associations were found between child emotional problems and parental PTSS, anxiety, and depression (r ≥ 0.36). Depressive symptoms and PTSS before the pandemic accounted for incremental variance in PTSS during the pandemic (in addition to sociodemographic variables and stress level during the pandemic). The findings suggest that the COVID-19 pandemic may also represent a traumatic event and parental PTSS may be significantly related to child stress, implying special consideration of family/family dynamics in times of crisis.