The current study investigates whether prepregnancy maternal posttraumatic stress disorder (PTSD) symptoms, depressive symptoms, and stress predict children's cortisol diurnal slopes and cortisol awakening responses (CARs) adjusting for relevant variables. Mothers were enrolled after delivering a baby and followed through their subsequent pregnancy with 5 years of longitudinal data on their subsequent child. This prospective design allowed assessment of PTSD symptoms, depressive symptoms, and perceived stress prior to pregnancy. Children provided three saliva samples per day on three consecutive days at two timepoints in early childhood (M age = 3.7 years, SD = 0.38; M age = 5.04 years, SD = 0.43). Mothers’ PTSD symptoms prior to pregnancy were significantly associated with flatter child diurnal cortisol slopes at 4 and 5 years, but not with child CAR. Findings at the age of 4 years, but not 5 years, remained statistically significant after adjustment for maternal socioeconomic status, race/ethnicity, child age, and other covariates. In contrast, maternal prepregnancy depressive symptoms and perceived stress did not significantly predict cortisol slopes or CAR. Results suggest that maternal prepregnancy PTSD symptoms may contribute to variation in early childhood physiology. This study extends earlier work demonstrating risk of adverse outcomes among children whose mothers experienced trauma but associations cannot be disentangled from effects of prenatal mental health of mothers on children's early childhood.