Health-related behaviours in children can be influenced by parental support programmes. The aim of this study was to explore barriers to and facilitators for the implementation of a parental support programme to promote physical activity and healthy dietary habits in a school context. We explored the views and experiences of 17 coordinating school nurses, non-coordinating school nurses, and school principals. We based the interview guide on the Consolidated Framework for Implementation Research. We held four focus group discussions with coordinating and non-coordinating school nurses, and conducted three individual interviews with school principals. We analysed data inductively using qualitative content analysis. We identified "Creating commitment in an overburdened work situation" as an overarching theme, emphasising the high workload in schools and the importance of creating commitment, by giving support to and including staff in the implementation process. We also identified barriers to and facilitators of implementation within four categories: (1) community and organisational factors, (2) a matter of priority, (3) implementation support, and (4) implementation process. When implementing a parental support programme to promote physical activity and healthy dietary habits for 5- to 7-year-old children in the school context, it is important to create commitment among school staff and school nurses. The implementation can be facilitated by political support and additional funding, external guidance, use of pre-existing resources, integration of the programme into school routines, a clearly structured manual, and appointment of a multidisciplinary team. The results of this study should provide useful guidance for the implementation of similar health promotion interventions in the school context.