Childhood exposure to stress can induce prolonged negative effects on health, which in turn confer risks for the next generation, but greater specificity is needed to inform intervention. A first step is to measure individual differences in emotional reactivity to stress early in life in ways that can account for heterogeneity in child exposure. The present study tested the hypothesis that mothers’ childhood exposure to stress would be differentially associated with patterns of positive and negative emotional reactivity in their offspring, suggesting transmission of stress response across generations. Participants were 268 young mothers (age 14–23 years) followed longitudinally since childhood, and their infants aged 3–9 months. Latent class analysis of infant emotions expressed before and during the still-face paradigm yielded five subgroups that varied in valence, intensity, and reactivity. After accounting for sociodemographic factors, infant temperament, and postpartum depression, multinomial regression models showed that, relative to an emotionally regulated still-face response, infants showing low negative reactivity were more likely to have mothers exposed to childhood emotional abuse, and infants showing high and increasing negative reactivity were more likely to have mothers exposed to childhood emotional neglect. Mechanisms by which early maternal stress exposure influences emotional reactivity in offspring are discussed.