The transgenerational effects of parental diagnoses, trauma and coping mechanisms on children's internalizing symptoms are not well understood. In a population-based study of 933 families combining data from a web-based survey and the Danish registers, we used an online survey of parents to examine how parental diagnoses, trauma and coping mechanisms affect the development of internalizing symptoms in children aged 6 to 18 years. To account for attrition, we used inverse probability weights in our regression models. Children of parents diagnosed with depression or anxiety displayed more internalizing symptoms than children of controls. Similarly, children of parents who experienced multiple trauma had significantly more internalizing symptoms. In contrast, we observed significantly fewer internalizing symptoms among children of parents who felt they could cope well. The protective effect of parental coping persisted even after adjusting for parental diagnoses or trauma. Interventions boosting parental coping mechanisms might help to prevent the development of internalizing symptoms in children even among patients who have been diagnosed with depression or anxiety or experienced a high trauma load.