This study investigated the association between inter-parental conflict at a single occasion, or repeated over early childhood, and children's internalizing and externalizing problems at 10-11 years; and examined potential mechanisms via social risk, maternal mental health, and parenting. Data were five time points from the Baby cohort of the Longitudinal Study of Australian Children (N = 3696, recruited in 2004). Verbal or physical inter-parental conflict was measured at 0-1, 2-3, 4-5, and 6-7 years. Internalizing and externalizing problems (Strengths and Difficulties Questionnaire) were measured via mother-, father-, teacher-, and child-report at 10-11 years. A series of regression models accounted for social risk at 0-1 years, parenting, and maternal psychological distress at 8-9 years. Physical and verbal inter-parental conflict (reported by 16 and 33% of mothers, respectively) consistently predicted mother-, father-, and child-reported externalizing and internalizing problems, and teacher-reported externalizing (but not internalizing) problems (adjusted regression coefficients [β] = 0.4-1.1). Repeated compared to single report of verbal conflict was associated with more behavior problems (adjusted mean = 0.8-1.1 compared to 0.4-0.6).Children are sensitive to inter-parental conflict, with long-term negative effects for child mental health even when reported at one time point within the first 6 years of life. What is Known: • Studies of children born prior to 1990 show that children exposed to verbal conflict or severe forms of family violence are at greater risk of mental health problems. What is New: • Physical and verbal inter-parental conflict reported once or at multiple time points over the first 6 years of life was associated with externalizing and internalizing problems reported by mothers, fathers, children, and teachers. • Associations between inter-parental conflict and child problems were not explained by family social risk, maternal mental health, or parenting.