Objectives Exposure to intimate partner violence (IPV) is known to challenge children's optimal development. This study sought to associate participants’ beliefs about IPV held during childhood with their adjustment as adults, and to compare their beliefs from childhood to their beliefs in early adulthood. Method A nationally representative sample of 703 Swedish young adults reported on their past and present beliefs about the causes of their parents’ IPV. Standardized measures assessed their mental health (anxiety, depression, and traumatic stress symptoms) and the quality of their relationships as adults. Results The most common explanations for IPV were that the perpetrator suffered from physical or mental illness, had relationship problems, or was distressed. Participants were less likely to blame themselves for IPV or to believe that the perpetrator was cruel when they were adults, compared to their reports of themselves as children. Women were more likely to attribute mental or physical illness as the cause of the perpetrator's IPV. Childhood beliefs that the perpetrator was debilitated (from mental illness or substance abuse) and cruel (took pleasure in violence and/or despised the child) were associated with greater mental health problems and poorer relationship quality in adulthood. Conclusion Evaluation of children's harmful beliefs about IPV could be useful in adapting intervention services aimed at ameliorating negative personal causal attributions.