Background. Research has shown that peer-group supervision can strengthen GPs' professionalism, but little is known about the individual learning processes. To establish professionalism beyond professional behaviour, identity and idealism need to be included. The inner attitudinal values of professionalism within the individual are, however, difficult to assess. Aim. On the basis of a multiple case study, this paper describes the process of professional learning and challenges for individual GPs, as they take part in supervision groups focusing on children cases. Methods and Results. By using a two-dimensional theoretical model, it is shown that all GPs developed their professional behaviour, and many of them strengthened their professional identity in this domain towards a changed professionalism. Most participants emphasized the positive experience of sharing worries with families indicating care and interest. Some participants learning processes were very linear/convergent; others were complex/divergent-starting out with a relatively simple objective, realizing how multifaceted the issue was after the first year leading to a final development of new perspectives or action possibilities. Conclusion. The composition of supervision groups, as well as the professional background of the supervisor, may play a significant role in the development of professional behaviour and professionalism.