Knowledge on how to improve public open spaces in deprived neighbourhoods to increase active living among children is scarce and comprehensively evaluated public open space interventions are needed. Firstly, the aim was to explore if involving 39 local fifth-grade children (10-11 years old) from a deprived neighbourhood in creating playable installations in a public open space influenced their use of this space. Secondly, we wanted to explore if the Reach, Effectiveness, Adoption, Implementation and Maintenance framework (RE-AIM) was useful for evaluating different stages in the intervention project. RE-AIM was applied through a convergent mixed-methods triangulation design using survey, accelerometer, GPS, and interviews as data sources. Effectiveness outcomes revealed that on average the space was used less by the 39 children after the intervention. The implementation and maintenance dimensions revealed aspects of why most children involved in the project did not use the space after intervention. The evaluation cast light on children's perceptions of their role, and importance of maintenance when the intervention was completed. In future, all dimensions of built environmental projects would benefit from being planned and evaluated in a collaboration with all project partners using an evaluation framework integrated and applied from the beginning of the project.