Despite the principle of the best interests of the child being enshrined in legislation, previous research and public reviews show that it is not always applied in social services work with children. This justifies the need for deeper knowledge of social workers' interpretations and use of professional discretion. The study aims to analyze how social workers, as street-level bureaucrats, interpret and justify the application of the principle of the best interests of the child in child welfare matters, as well as how they perceive that they ensure children’s participation in their work. This was a qualitative study conducted through semi-structured interviews with eight social workers. The results show that the application of the principle of the best interests of the child in child welfare cases largely depends on the social workers’ professional assessments and discretion. While structures such as legislation and the BBIC framework provide support for involving the child, organizational conditions, such as lack of collaboration, time constraints and limited resources restrict the possibility of fully satisfying the child’s best interests.