Background
Early Childhood Education and Care (ECEC) teachers at urban preschools are potential key figures to promote healthy behaviours in disadvantaged young children and to engage parents in lifestyle-related topics. An ECEC teacher-parent partnership regarding healthy behaviours may support parents and stimulate their children’s development. However, it is not an easy task to establish such a collaboration and ECEC teachers need tools to communicate with parents about lifestyle-related topics. This paper describes the study protocol of a preschool-based intervention (CO-HEALTHY) to promote an ECEC teacher-parent partnership regarding healthy eating, physical (in)activity and sleeping behaviours in young children.

Methods
A cluster randomised controlled trial will be performed at preschools in Amsterdam, the Netherlands. Preschools will be randomly allocated to an intervention or control group. The intervention consists of a toolkit with 10 parent-child activities and associated training for ECEC teachers. The activities were composed using the Intervention Mapping protocol. At intervention preschools, ECEC teachers will carry out the activities during standard contact moments. Parents will receive associated intervention materials and will be encouraged to perform similar parent-child activities at home. At control preschools, the toolkit and training will not be implemented. The primary outcome will be the teacher- and parent-reported partnership regarding healthy eating, physical (in)activity and sleeping behaviours in young children. The perceived partnership will be assessed by a questionnaire at baseline and at 6 months. In addition, short interviews with ECEC teachers will be held. Secondary outcomes include the knowledge, attitude, food- and activity-related practices of ECEC teachers and parents. Furthermore, children’s eating, physical (in)activity and sleeping behaviours, and weight development will be assessed. A process evaluation of the intervention will be made.

Discussion
The intervention aims to provide a practical tool for ECEC teachers at urban preschools to promote an ECEC teacher-parent partnership regarding a healthy lifestyle in young children.

Trial registration
Netherlands Trial Register (NTR): NL8883. Date registered: September 8, 2020.