This study examined relationships among parents' physiological regulation, their emotion socialization behaviors, and their children's emotion knowledge. Parents' resting cardiac vagal tone was measured, and parents provided information regarding their socialization behaviors and family emotional expressiveness. Their 4- or 5-year-old children (N = 42) participated in a laboratory session in which their knowledge of emotional facial expressions and situations was tested and their own resting vagal tone was monitored. Results showed that parents' vagal tone was related to their socialization behaviors, and several parent socialization variables were related to their children's emotion knowledge. These findings suggest that parents' physiological regulation may affect the emotional development of their children by influencing their parenting behaviors. (Contains 2 tables.)