Background Children born to mothers who were younger than average at their first childbirth are at increased risk for future persistent delinquent behaviour, but explanations for this remain unclear. Aims Our aim was to identify possible family and parenting variables that may help explain this relationship. We hypothesised that parental stress, large number of children in the home, low socioeconomic status (including neighbourhood problems) and poor parenting would account for the link between early first motherhood and their offspring's delinquency. Methods Four hundred and sixty‐two boys were selected from the Pittsburgh Youth Study, a longitudinal study of a random sample of school boys in Pittsburgh, initially assessed half‐yearly and then annually from 7 to 19 years of age, using self‐reporting and other reporting methods. Indirect effect models were used to test relationships between variables. Results Higher levels of parental stress, poorer parent–child communication and caring for a larger number of children all mediated the relationship between maternal youth and persistent delinquency by their boys, but only explained about 20% of it. Discussion At least partial explanations of the relationship between a mother's age at first childbirth and persistent delinquency in her male offspring suggest that future research should test whether early interventions with younger mothers to decrease their sense of stress in parenting and improve their capacity for communication with their child(ren) may help to prevent persistent delinquency in their boys. Programmes designed to help young women make more informed and planned decisions about their pregnancies should also be evaluated. Copyright © 2015 John Wiley & Sons, Ltd.