Cooperation between preschools and parents is one key dimension of pedagogical quality in early childhood education and care (ECEC). We examined the structural characteristics of ECEC that predict preschool cooperation activities and how they are associated with children's language and social-emotional skills at the age of 3. The results are based on data of an evaluation study with a sample size of 146 families and 46 preschool centres. The head teachers of the preschools gathered information about cooperation activities via a questionnaire. Children's language and social-emotional skills were assessed using the Peabody Picture Vocabulary Test (PPVT), the Vineland Adaptive Behavior Scale (VABS), and the Strengths and Difficulties Questionnaire (SDQ). Results showed associations between further training, job experience, and parent involvement activities. Furthermore, teachers reported that a positive association was found between cooperation activities and problematic behaviour and between receptive language and prosocial skills of the children. Attention should be paid to the professionalization of parent-preschool cooperation.