This thesis explores how a norm-critical design approach can support the transformation of norms surrounding child participation in care contexts, with a focus on paediatric and social care. It illustrates how such an approach can generate impact in care contexts if applied in related research and tool development. Since a persistent gap remains between the ambition of increased child participation and its realisation in practice, it poses the questions: How can barriers to child participation in care be understood based on the perspectives of key actors? and How can a norm-critical design approach facilitate a shift in norms related to child participation in care, design, and research contexts? Rooted at the intersection of design, critical theory, and health science, the thesis applies a sociotechnical perspective on participation. It compiles five qualitative studies involving children and young adults, parents, care professionals, nursing students, and nursing teachers. Together, the studies provide practical insights into how design can counteract exclusionary norms and structures in care, design, and research contexts—contexts that are still largely defined by adult-centric and biomedical paradigms. The results underscore the importance of enabling children's voices when shaping the systems meant to support them, and putting the spotlight on norms, situated perspectives, and power positions when designing for participation. The comprehensive understanding includes a theoretical model visualising the role of norm-critical approaches in norm change and suggests four ways for design to facilitate norm transformation. While norm-critical design approaches have previously not been used to address the issue of child participation in care, this thesis shows great potential for such approaches to generate impact in care contexts if applied in related research and tool development.