Behavioral activation (BA) effectively treats depression in adults, and shows promise in treating anxiety. Research into its application to children and adolescents is emerging. This review aimed to explore the scope of studies, current evidence of effectiveness and how the intervention has been delivered and adapted, to inform future research. A systematic review was undertaken searching PsycInfo, PubMed including Medline, EMBASE, and Scopus for terms relating to BA and children and adolescents. Two researchers scored abstracts for inclusion. Data extraction was completed by one researcher and checked by another. 19 studies were identified, across 21 published articles. 12 were case studies, with three pre–post pilot designs and four randomized-controlled trials. Case studies found early support for the feasibility and potential effectiveness of BA to address both anxiety and depression. The RCTs reported largely positive outcomes. Meta-analysis of depression scores indicated that BA may be effective; however, high heterogeneity was observed. Sample sizes to date have been small. BA has been delivered by trained therapists, doctoral trainee psychologists, social workers, or psychology graduates. Studies are uniquely in high-income settings. Adaptations include flexibility in content delivery, youth friendly materials, and parental involvement. There is some limited evidence to support BA as effective for young people. Feasibility and acceptability are supported. Fully powered trials are now required, with expansion to delivery in low- and middle-income settings, and detailed consideration of implementation issues that consider culture and environment.