PurposeThe postnatal period is a vulnerable time for parents and children but epidemiological and health care utilisation data for Germany on parental mental health during early childhood is scarce. This protocol describes the rationale, aim and study design of a population-based cohort study to assess the occurrence and determinants of psychosocial stress and mental health disorders, as well as the use and cost of health care and social services in early childhood.MethodsAs part of the collaborative SKKIPPI project, we will contact a random sample of 30,000 infants listed in the residents’ registration offices of three German towns and we expect to include 6,000 mother–child pairs. Both parents are invited to fill out an online screening questionnaire. Mothers with indications of psychosocial stress will be interviewed to assess mental health disorders, regulatory problems of their children, as well as health care and social services utilisation, with a follow-up assessment after 6 months.ResultsAfter description of sociodemographic and health data, we will analyse occurrences, patterns, and potential determinants (maternal age, social status, household factors, migration status etc.) of psychosocial stress and mental health disorders in the mothers and their children in early childhood.ConclusionsOur study will identify potential risk and protective factors for postnatal mental health and health care utilization of psychosocially burdened families. This will help to improve prevention and treatment strategies to strengthen the parent–child relationship, to reduce persisting vulnerability of children, and to improve health care and social services.Trial registrationThe study has been registered in the German Clinical Trial Registry on February 8th 2019 (DRKS-ID: DRKS00016653).