The aim of this study was to understand how a social workers responsible for foster children within the municipal social services, is working with the children’s continuous relationships with family members and other significant related, as well as which knowledge formed the basis for their work practice. The study is based on interviews with eight social workers from three different municipalities. The results showed that the work is based on the law which causing interpretations, in which the individual assessment is in fact to be based on the child's needs- and best, but in practice are decisions made by and involving several parties. The study showed that the guardians and foster cares wills and opinions weigh heavily, often at the expense of the child perspective. As a strategy to assess the child's best, the social workers turn to their own quiet knowledge and colleagues and the organization's traditions to retrieve knowledge that supports the decisions, and to a lesser extent to scientific knowledge and evidence-based practice. The social workers also expressed a wish to work more with scientific underpinnings, but the organization does not work with routine gathering of scientific knowledge.