INTRODUCTION: Parents with intellectual and developmental disabilities (IDDs) often need parenting support, but there are few evidence-based programmes adapted to their cognitive needs. Parenting Young Children (PYC), a home-based programme for parents with IDDs, is perceived as beneficial by parents and practitioners, but it is unclear if PYC improves parenting. The purpose of the proposed mixed-methods study is therefore to evaluate the PYC programme for improved parenting in parents with IDDs. METHODS AND ANALYSIS: The quantitative evaluation will have a multi-centre, pretest-posttest study design and include parents with IDDs (children aged 0-9) in need of adapted parenting support. Goal-attainment in parenting skills, parental self-efficacy and child mental health will be measured outcomes. Interviews will be used to explore the perspectives of parents and children on PYC. ETHICS AND DISSEMINATION: Particpation is based on informed consent from parents and guardians of the participating children. Ethical approval was granted by the Swedish Ethical Review Authority.