Background: Postpartum maternal anxiety and depression can affect child development and family functioning. However, the long-term impact of postpartum maternal anxiety and depression on child and paternal mental health is understudied. The present large-scale prospective cohort study is one of the first to investigate whether maternal anxiety and depressive symptoms postpartum and at child age 5-6 years separately and synergistically increase paternal anxiety and depressive symptoms and child emotional problems in early adolescence at age 11-12 years. Secondly, we investigated whether concurrent paternal anxiety and depressive symptoms at child age 11-12 years moderated the association between maternal anxiety and depressive symptoms in the postpartum period and at child age 5-6 years with child emotional problems at age 11-12 years. Methods: This study is part of the Amsterdam Born Children and Development (ABCD) cohort study, the Netherlands (N = 2.298). Maternal postpartum anxiety and depressive symptoms were assessed using the State-Trait Anxiety Inventory (STAI) and the Center for Epidemiologic Studies Depression Scale (CES-D) at 13 weeks postpartum. Maternal anxiety and depressive symptoms at child age 5-6 years and parental anxiety and depressive symptoms at 11-12 years were assessed using the Depression Anxiety Stress Scale (DASS-21). Child emotional problems were reported by the child and a teacher using the Strengths and Difficulties Questionnaire (SDQ). Multivariable linear regression was conducted, adjusted for demographic, perinatal/obstetric confounders, and affective symptoms of the other family members at 11-12 years. Results: Neither maternal anxiety nor depressive symptoms were related to paternal depressive symptoms at child age 11-12 years, while maternal postpartum depressive symptoms, depressive symptoms at 5-6 years and maternal anxiety at 5-6 years were