People who commit sexual offences are a heterogeneous group, with research suggesting that children and young people commit a large proportion of all sex offences, especially those committed against other children. This systematic review provides a synthesis of literature concerning the characteristics of children and adolescents who exhibit harmful sexual behaviour. There is a particular focus in this review on studies that examine the characteristics of children and young people exhibiting these behaviours within institutional and organisational settings or which take a situational and/or developmental approach to understanding sexually abusive behaviour. Using a developmental and life-course criminology lens, this review explores implications from the literature for the prevention and response to child sexual abuse, with a particular focus on institutional contexts where the perpetrators are children and adolescents.