Childhood trauma experiences can carry over to the next generation, affecting the health and behavior of survivors' children. However, the mechanisms underlying these intergenerational effects of childhood trauma are not yet clear. One mechanism may be changes in children's hypothalamic-pituitary-adrenal (HPA) axis. This preregistered longitudinal study examined associations between 170 mothers' childhood trauma experiences (maltreatment, family and peer violence) and their children's cortisol reactivity and total circadian cortisol output at 12 months and 6 years of age. Multilevel regression analyses revealed that maternal childhood trauma was not significantly associated with child cortisol reactivity or total circadian cortisol output, neither at 12 months nor at 6 years of age. Thus, we found no evidence in this community sample that maternal childhood trauma impacts young children's HPA axis functioning. Exploratory analyses revealed moderation effects of maternal prenatal psychopathology and prenatal circadian cortisol slope: in mothers with high prenatal psychopathology or circadian cortisol slope, maternal childhood trauma was positively associated with child total circadian cortisol output, while this association was negative in mothers with low psychopathology or circadian cortisol slope. Future research should replicate these findings in older children and more severely trauma-exposed populations and further explore moderators of this intergenerational association.