Background: Children with mild intellectual disabilities and emotional and behavioural problems whose parents have mental health concerns are at an increased risk of developing problems themselves. This study analysed the effectiveness of the 'You are Okay'-program aimed to support these children and parents and to reduce the risk of problem development in children. Method: A quasi-experimental design was used to compare the experimental group ('care as usual' and 'You are Okay') with the control group ('care as usual') on the main outcome of emotional and behavioural problems and proposed intermediate outcomes. Results: Children in the experimental group reported a significant medium to large decrease in emotional and behavioural problems compared to the control group. The effects on the intermediate outcomes were non-significant. Conclusions: This specific study population comprising a vulnerable group of children seems to benefit from this specially adapted 'You are Okay'-program. More research is necessary to draw further conclusions.