This paper explores the ways in which social worker practitioners conceptualise childhood and the significance of this for developing social work practice. The data was generated through qualitative semi-structured interviews and group discussions with practitioners who were working directly with children in child protection or children's service centres in Iceland. The interviews formed an initial stage of an action research study, informed by young people who had interacted with social services, and designed to develop practice in line with the young people's views and expectations. The findings indicated there were contrasting and co-existing conceptualisations that had different implications for children. On the one hand, conceptualisations of children as problems and children as incompetent appeared, from practitioner's accounts, to have undermined children's ability to present their own concerns and maintain control over what happened to them. In contrast, conceptualisations broadly characterised as children active in defining problems and children participating on an equal footing appeared to assist practitioners in being prepared to promote children's active involvement in defining problems and finding solutions. The analysis suggested that how practitioners think about children is an important area of enquiry and highlighted the shift in thinking required to develop more effective participatory practice.