Introduction: Paediatric patients with disorders that involve brain functioning are particularly vulnerable with respect to including them in shared decision-making. Current tools are mostly paper or digital patient information. We lay the groundwork for improving engagement with a concept that we coined ‘the Self-Portrait’. The main goals were to identify (1) obstacles and (2) design parameters that enable patient participation. Methods: A research-through-design approach was utilized in nine patients with brain-related disorders (4–12 years), 15 parents and 15 medical professionals, involving contextual research (interviews and observations) within the paediatric hospital and patients' homes and codesign. Sensitizing materials and early instances of design solutions were deployed as catalysts for communication. Five rounds of enriched interviews and design reviews were thematically analysed to answer the research questions. Results: Obstacles to child involvement were related to children's level of understanding, the time and energy necessary for information processing and lack of perceived relevance of the information. Patients' engagement is supported by design features that extend the time frame of interaction beyond the consultation, transfer information interactively and give control and influence during the consultation. Conclusion: Obstacles were detected that complicate child engagement, which differ between stakeholders. Promising design features were identified that have the potential to play an important role in enabling active child involvement. These findings show that applying principles of human-centred design research and codesign can bring together patients, parents and medical professionals around a tool that provides a shared language and focus, which are prerequisites to increase child engagement. Patient or Public Contribution: Patients, parents and clinicians contributed as design informants during contextual research and design reviews. Clinicians provided feedback on the initial outcomes of thematic analysis. Two researchers assisted in consensus sessions during the thematic analysis.