Introduction: Family centres in Sweden are integrated services that reach all prospective parents and parents with children up to their sixth year, because of the co-location of the health service with the social service and the open pre-school. The personnel on the multiprofessional site work together to meet the needs of the target group. The article explores a program theory focused on the open preschools at family centres. Method: A multi-case design is used and the sample consists of open pre-schools at six family centres. The hypothesis is based on previous research and evaluation data. It guides the data collection which is collected and analysed stepwise. Both parents and personnel are interviewed individually and in groups at each centre. Findings: The hypothesis was expanded to a program theory. The compliance of the professionals was the most significant element that explained why the open access service facilitated positive parenting. The professionals act in a compliant manner to meet the needs of the children and parents as well as in creating good conditions for social networking and learning amongst the parents. Conclusion: The compliance of the professionals in this program theory of open pre-schools at family centres can be a standard in integrated and open access services, whereas the organisation form can vary. The best way of increasing the number of integrative services is to support and encourage professionals that prefer to work in a compliant manner. (author abstract)