A transition in care (TIC) refers to a significant change in the primary adults responsible for a child’s care, often involving shifts to non-parental settings, such as kinship or foster care. This paper explores three main points: the importance of including infants and children experiencing TIC in longitudinal studies of child health and development; the relevance of these children in research on parental substance use; and effective methods for tracking children undergoing TIC. The authors highlight the HEALthy Brain and Child Development (HBCD) study as a model for retaining these children in research. Strategies include documenting the frequency and contexts of TIC, understanding consent and reporting requirements, being aware of child welfare policies, addressing retention challenges, emphasizing diversity and inclusion, and establishing adaptable methods for monitoring these children’s progress as they age.