Inclusion of children in medical decision making, to the extent of their ability and interest in doing so, should be the default position, ensuring that children are routinely given a voice. However, optimizing the involvement of children in their health care decisions remains challenging for clinicians. Missing from the literature is a stepwise approach to assessing when and how a child should be included in medical decision making. We propose a systematic approach for doing so, and we apply this approach in a discussion of two challenging clinical cases. The approach is informed by a literature review, and is anchored by case studies of teenagers’ refusal of clinical care, regulatory requirements for research assent, and the accepted approach to involving cognitively impaired adults in medical decisions.