The present study investigated what explains and accounts for first pre-pubescent delinquent behaviors among children. This was based on the notion that a developmental paradigm (e.g., self-control) alongside family socio-economic status (SES) can provide a passable explanation for the first and early delinquent behavior. A nationally representative sample of eighth graders (N = 3,449, 50% boys) from the Korea Youth Panel Survey (KYPS) was reviewed in terms of first delinquent behaviors. Results revealed that pre-pubescent boys started to drink at an earlier age than girls, whereas pre-pubescent girls engaged in relational bullying earlier than their male counterparts. Children’s onset of delinquency age was inversely associated with family SES, but was positively associated with their degree of self-control. Different types of first delinquency were distinguished by levels of parental education as well as child’s self-control. Implications of the findings are discussed.