This is a pilot non-randomised controlled trial. The study was approved by the Newcastle University Research Ethics Committee (application number:01223/9764/2016). The intervention consists of a one-day course given by specialist providers, specifically for those who work with children under 5. The training consisted on helping practitioners around fundamental movement skills (balancing, jumping throwing, catching kicking) and helping them to develop a better understanding about the importance of physical activity for early years. The training also covered an introduction to the United Kingdom (UK) physical activity guidelines and how practitioners could translate the physical activity guidelines into practice. The course used an ecological model approach in the delivery of the intervention. The programme provided ideas for: creating enabling environments for physical activity; planning physical activity for all stages of development; balance child-initiated and adult-led physical activities; encourage parent and carer support and promotion of physical activity beyond the nursery setting. Data collection took place between February 2017 and June 2018. All nurseries and schools with nurseries in the Middlesbrough area were eligible to participate and were invited to take part.

The following measures were intended to be collected pre-intervention and 6 months post-intervention (follow-up). Practitioner behaviour was assessed by direct observation adapted from the Communication Supporting Classroom Observation Tool. Each observation lasted approximately 30 min and was conducted by one of the researchers. Knowledge of the physical activity guidelines and benefits of physical activity for early years was assessed by a customised questionnaire. Intentions for behaviour change was assessed by a questionnaire which covered the following domains: Knowledge; Skills; Social/Professional Role \& Identity; Belief about Capabilities; Optimism; Beliefs about Consequences; Intentions; Goals- Action Planning; Goals - Priorities; Memory, Attention \& Decision Processes; Environmental Context \& Resources; Social Influences; Emotion; Behavioural Regulation; Social \& Professional Role; Work Environment. Children. Physical activity was measured directly using a thigh-mounted accelerometer (activPAL) which has been validated in young children. Time in sitting, standing and stepping postures was measured during school or nurseries hours. Data were recorded in 15 s epoch and reduced to the percentage of wear time in each of the postures, to account for potential differences in wear time within and between participants. Height (to 0.1cm) and weight (to 0.1kg) were measured twice without socks or shoes, in indoor clothing. BMI was then derived, and z -scores created relative to UK 1990 data. Fundamental movement skills were assessed with the Movement Assessment Battery for Children 2 (Movement ABC-2) which covers fine and gross motor tasks, manual dexterity and balance. Process evaluation. Using focus groups, interviews and a questionnaire with all stakeholders explored the reasons for participation/non-participation of practitioners and families; participants' views and perceptions of the intervention in terms of acceptability, feasibility and usability. All data were exported to SPSS for analyses. Descriptive statistics for all variables of interest were generated