Importance: In adulthood and adolescence, mental health vulnerability is known to be associated with risk of criminal justice system contact as both a perpetrator and survivor of crime, but whether this association is apparent early in child development is unknown. Prevention of poor outcomes, including repeated contact with the criminal justice system, relies on the identification of vulnerability early in life and at the start of such contact. Objective: To ascertain whether children with emotional or behavioral problems and general developmental vulnerabilities are at an increased risk of subsequent contact with police as a person of interest, a survivor of crime, or a witness. Design, Setting, and Participants: This cohort study used routinely collected data from the New South Wales Child Development Study in Australia. The cohort was composed of children who entered full-time schooling in New South Wales in 2009, had complete data for the emotional maturity domain of the Australian Early Development Census, and had no police contact before January 1, 2009. The children in the cohort were followed up until the age of 13 years. Data were analyzed from October 17, 2019, to May 13, 2020. Exposures: Emotional or behavioral problems and developmental risk profiles derived from the teacher-rated Australian Early Development Census. Main Outcomes and Measures: Incidence rates of police contact (as a person of interest, survivor of crime, or witness) were derived from the New South Wales Police Force Computerised Operational Policing System. Results: A total of 79 801 children (40 584 boys [50.9%]; 2009 mean [SD] age, 5.2 [0.37] years) were included. Children with teacher-identified emotional or behavioral problems at school entry had an incidence rate of police contact (for any reason) that was twice that of children without such problems (unadjusted hazard ratio [HR], 2.14; 95% CI, 1.94-2.37). Contact with police as a survivor of crime was most commonly recorded (7350 [9.2%]), but the strength of the association was greatest between emotional or behavioral problems and police contact as a person of interest (unadjusted HR, 4.75; 95% CI, 3.64-6.19). Incidence of police contact as a person of interest was high for children with a pervasive developmental risk profile (unadjusted HR, 13.80; 95% CI, 9.79-19.45). Conclusions and Relevance: This study found an association of emerging emotional or behavioral problems and developmental vulnerabilities with increased risk of police contact for any reason among young children, suggesting that this well-known association in adults and adolescents can be identified at an earlier developmental stage. These findings support primary and secondary interventions to prevent police contact early in life and to target the earliest contacts with the criminal justice and educational systems.