The authors first review and compare the findings of previous self-report studies regarding the prevalence of children's (ages 7-12) delinquent behavior. This review encompasses changes in the prevalence and seriousness of child delinquency over the past two decades. It concludes that the prevalence of delinquent offending by children has not changed much over this period. Using the authors' own ongoing studies of self-reported delinquency by children, the chapter addresses the age of onset and development patterns of delinquency in this population. The types of delinquent behavior that resulted in police contacts are then identified, since this information may indicate the types of child offenders who enter the juvenile justice system. Overall, self-reported delinquency data indicate that it was widespread during childhood, often beginning early; this was especially true for minor forms of aggression. Delinquent behavior was limited to childhood for many youths, but extended into the teen years for other youths. Approximately one-third of the 7-12-year-olds were not involved in any form of delinquency when minor aggression/assaults were excluded. Nearly one-third were involved in only one type of delinquency, i.e., minor assaults, property offenses, or drug use. The remaining one-fifth to one-third were involved in multiple types of offenses. Recommendations are offered for future research in this area. 5 tables and appended items included in delinquency subscales for the Program of Research on the Causes and Correlates of Delinquency