There is a large body of literature that has considered children and adolescents' psychosocial development in youth sport contexts. Two particularly extensive research areas include the study of positive youth development through sport (Holt, 2016), and the study of athletes' transitions throughout the athletic pathway (Stambulova & Wylleman, 2015). While much of the research is informed by holistic and lifespan developmental approaches, it is currently unclear the extent to which studies in these intersecting areas of youth sport research have drawn on theories from child and adolescent developmental psychology more broadly. The purpose of this study was to conduct a scoping review of the literature on positive youth development and youth athlete transitions in sport, to investigate the use of child development theory in research across these areas. Two databases were systematically searched (APA PsychINFO and SportDiscus) and 12,503 abstracts were screened for inclusion in the review (inclusion criteria: full text empirical articles, English language, research conducted with athletes 16 years and younger). Included articles are analyzed according to Sandelowski's (1993) conceptualisation of the uses of theory in research, including the centrality and temporal placement of theory, and the function of any theories used. This presentation will provide: an overview of the theories that have informed youth sport research to date such as social cognitive theory (Bandura, 1986) and theory of identity (Erikson, 1968) among others, an evaluation of how theory has been used, and future avenues for the cross-pollination of youth development and youth sport research.