Background Participation in sports is associated with numerous physical and psychosocial health benefits, however, participation declines with age, and knowledge of perceived barriers to participation in children is lacking. This longitudinal study of children and adolescents aimed to use the ecological model of physical activity to assess changes in barriers to participation in sports clubs to identify age-specific and weight-specific targets for intervention. Methods Longitudinal study -Perceived barriers to sports participation were collected from a birth cohort, the Gateshead Millennium Study (n>500) at ages 9 and 12 years. The open-ended question 'Do you find it hard to take part in sports clubs for any reason?' was completed with free text and analysed using content analysis, and the social-ecological model of physical activity. Results Barriers from across the social-ecological model were reported. Barriers at 9 years were predominantly of a physical environmental nature, and required high parental involvement (for transport, money, permission), or were associated with a lack of suitable clubs. At 12 years, perceived barriers were predominantly classed as intrapersonal ('they're boring') or social environmental ('my friends don't go'). Perceived barriers were not associated with weight status. Conclusions Perceived barriers to sports participation change rapidly in childhood and adolescence. Future interventions aiming to increase sports participation in children and adolescents should target specific age groups, should consider the rapid changes which occur in adolescence, and aim to address prominent barriers from across the socioecological model. Perceived barriers may be unrelated to current weight status, allowing for more inclusive solutions.