This study analyzes informal learning, drawing on video recordings of staff-child interaction in a pediatric unit. It is shown that even very young patients engage in intent community participation, carefully noting fine variations in examination and treatment practices. They orient to everyday routines in successively more complex ways, gradually acquiring novel repertoires of practices; advancing from nonverbal uptake to an active use of medical terminology, and to actively assisting staff members. Ultimately, the children themselves assume almost full responsibility for routine procedures. The unit had adopted partnership-oriented routines, and the doctors and nurses spent much time in securing the children's consent and participation in their own treatment. In contrast to much earlier work in pediatric settings which has shown children to be marginal participants; even the youngest patients were engaged, and they successively acquired a set of novel practices related to treatment procedures. Together with doctors and nurses, the children could be seen to form a community of practice. But community is not something fixed; instead it is seen as an emergent phenomenon, dependent on staff members' and children's mutual alignments and collaborative action. Learning is thus analyzed as a social and relational phenomenon.