Sport has rarely been addressed in childhood studies' research, while sport research has only started to call attention to concepts from childhood studies. This article brings both fields together, to explore children's practices of agency and potential consequences for their wellbeing in organised sport. Such insights are timely, with widespread efforts to increase children's engagement in sport for its physical and mental health benefits, while recent reports identify wellbeing risks to children who participate. This article draws on case study research from a rugby club in England involving observations of training sessions, followed by interviews and discussions with 31 players aged 14-18, their parents, coaches and officials. Using Leonard's 'generagency', the article explores how the dominant motif of the 'rugby family' influenced children's practices of agency, creating a lattice for trusting relations between children, their parents and coaches. The findings dismantle an unduly individualistic concept of agency, highlighting how relations of trust and emotional affect can be protective and problematic in protecting children from harm or injury. The study underlines the necessity for dialogue and knowledge, in addition to the benefits of belonging, to support children's practices of agency and their wellbeing in sport.