Study protocol for Active Start Active Future: a randomised control trial of an early behaviour-change intervention targeting physical activity participation and sedentary behaviour in young children with cerebral palsy living in South East Queensland, Australia.

Introduction: The benefits of physical activity (PA) are compelling for all ages and abilities. For children with cerebral palsy (CP), two distinct health behaviours, being physically active and reducing sedentary time, are critical to target as an early intervention to reduce long-term morbidity. One approach may be to increase PA participation by empowering parents who are key to making family lifestyle changes. This study will compare Active Start Active Future, a participation-focused intervention, to usual care in a mixed-methods randomised waitlist-controlled trial.

Methods and analysis: A total of 40 children with CP (3-7 years), classified in Gross Motor Function Classification System (GMFCS) levels II-V, will be stratified (GMFCS II vs III, IV vs V) and randomised to receive either (1) Active Start Active Future, an 8-week intervention for 1 hour per week in any setting or (2) usual care followed by delayed intervention. Active Start Active Future aims to increase PA and reduce sedentary behaviour of young children with CP by providing participatory opportunities to promote PA behaviour change. Outcomes will be measured at baseline (T1), immediately postintervention at 8 weeks (T2) and at 26 weeks postbaseline (T3). The primary outcomes are the Canadian Occupational Performance Measure for both child and parent participation goals and child physical performance goal. Secondary outcomes include daily time spent in moderate to vigorous PA and sedentary time, gross motor function, quality of life, barriers to participation for the children and parents' PA and sedentary time. Intervention acceptability and experiences of PA participation will be explored using a qualitative descriptive approach.

Ethics and dissemination: The Children's Health Queensland Hospital and Health Service Human Research Ethics Committee (HREC/23/QCHQ/100850) and The University of Queensland Human Research Ethics Committee (2024/HE000054) have approved this study. The results of the study will be disseminated to families and community agencies as guided by our advisory group and as conference abstracts and presentations, peer-reviewed articles in scientific journals and institution newsletters and media releases.

Trial registration number: ACTRN12624000042549, Universal Trial Number: U1111-1300-7421; Australian New Zealand Clinical Trials Registry.