The Happy Healthy Active Children (HHAC) initiative is a multicomponent community-based initiative aimed at promoting physical activity, food literacy and nature literacy among children in early childhood kindergarten and primary school settings. Developed in collaboration between Activity Experts and Community Stakeholders, HHAC integrates thematic activities (Play, Nature, Food) across kindergartens, schools and the broader community. The initiative responds to growing concerns about declining physical activity levels, insufficient contact with nature and poor dietary habits in childhood, factors known to influence long-term health and well-being. This protocol outlines the design, implementation and planned evaluation of the HHAC initiative.

HHAC is carried out within the long-term strategic initiative Tingbjerg Changing Diabetes. Following the Supersetting approach, HHAC addresses inequity in health by mobilising resources across local settings (kindergartens, schools and the local community arenas) and population groups (children, parents, staff and other community members) to develop and implement contextually relevant activities promoting outdoor play, cooking and nature experiences. Activities are evaluated using a within-subject design in kindergartens, while in schools a quasi-experimental design with matched control groups is applied. Data is collected at baseline and follow-up through accelerometry, validated questionnaires and structured observations. Primary outcomes include physical activity levels, food literacy and nature literacy. Analyses apply linear mixed-effects models to account for repeated measures and clustering at the institutional level. The evaluation also investigates implementation processes and context-mechanism configurations through a comprehensive realist evaluation. This includes developing a programme theory, conducting interviews with children, parents, staff and other local stakeholders and participant observations aiming to explore experiences and the mechanisms through which the activities contribute to changes in behaviour and well-being. All data will be analysed and condensed for a model for transferability.

Findings will be disseminated through peer-reviewed journals, conference presentations and public engagement activities targeting educators, policymakers and health professionals. The intervention materials will also be made freely available to support broader implementation. The study procedures were registered and approved by The Capital Region’s centre for data reviews ‘Videnscenter for Dataanmeldelser’ (Reference: P-2023–14277). All procedures were carried out under relevant regulations and guidelines. Written information about the study was given to all school principals, teachers and parents/guardians before the start of the study, and written informed consent is obtained from all legal guardians of all participants in their native language prior to child enrolment.