This qualitative evidence synthesis aims to show how the agency and voices of minor children of parents with a mental illness (COPMI) or with an addiction (COPA) are represented in existing qualitative research. A thematic analysis was conducted to analyse the parts of the articles reporting on the voices of COPMI/COPA themselves (e.g., through interviews with them). Special attention was given to how the authors of the different articles represented children's agency and amplified their voices. The four themes found were secrecy and privacy, lack of information, fear and worry and informal care. Thus, these are the topics most commonly discussed by COPMI and COPA themselves. They both spoke of themselves as victims and as agents, and these two were strongly intertwined in their descriptions of their experiences and situations. The most important recommendation for policy, practice and research based on these results is that it is important to listen to what minor COPMI/COPA have to say about their own situation and see them not only as a victim of this situation but also as an agent.