BACKGROUND: Parental offending and mental illness are associated with an increased risk of criminal behaviour in offspring during adolescence and adulthood, but the impact of such problems on younger children, including children's experiences of victimisation, is less well known. AIM: To investigate the associations between parental offending and mental illness recorded prior to their offspring's age of 5 years and their offspring's contact with police as a 'person of interest', 'victim' or 'witness' between ages 5 and 13 years. METHODS: Our sample consisted of 72,771 children and their parents drawn from the New South Wales Child Development Study, an Australian longitudinal population-based record linkage study. Logistic regression analyses were conducted to examine associations between parental factors and offspring's police contact. Separate models examined the relationships between maternal or paternal offending and mental illness, as well as the combination among either or both parents, as the independent variables, and their child's police contact as the dependent variable. RESULTS: Parental offending and mental illness were each individually associated with indices of police contact among offspring. Stronger associations were observed when both offending and mental illness were present together (in either parent, or when one parent had both exposures). Stronger associations were evident for mothers with both factors across all offspring police contact types, relative to fathers with both factors, in fully adjusted models; that is, children of mothers with both factors were over four times as likely to have contact with police as a 'person of interest' (OR = 4.29; 95% CI = 3.75-4.92) and over three times as likely to have contact as a victim (OR = 3.35; 95% CI = 3.01-3.74) or witness (OR = 3.58; 95% CI = 3.03-4.24), than children whose mothers had no history of offending or mental illness. CONCLUSIONS: Children with a parental history of offending and mental illness in early life are at an increased likelihood of early police contact as young as 5-13 years of age; it is vital that this is taken as a signal to help them and their affected families according to need.