Previous research focusing on preschoolers’ healthy behaviors looked at developing interventions for separate behaviors, such as physical activity and sedentary behavior. Currently, there is a shift in research towards focusing on an integrated approach regarding the behaviors conducted in a 24-hour day, since targeting multiple behaviors is more effective. Activities in a 24-hour day consist of physical activity, sedentary behavior and sleep. Only very few Belgian preschoolers (10%) meet the guidelines regarding a healthy 24-hour day. Therefore, interventions focusing on all three behaviors with an integrated approach are needed. Since preschool children spend most of their time at school and at home, and engage in play-based learning in those settings, this project will develop and evaluate an intervention focusing on those 24-hour behaviors both at school and at home. The aim of the intervention is to increase the percentage of preschoolers that comply with the guidelines regarding a 24-hour day. Within the project, we will work closely together with both preschoolers’ teachers and parents to develop and create the intervention, framed within the Intervention Mapping protocol. The intervention will be evaluated through a cluster randomized controlled trial, using a pretest, posttest and follow-up. Preschoolers’ physical activity, sedentary behavior and sleep will be measured using objective measurement devices (ActivPAL) and using questionnaires filled in by the parents.