Interoception, often defined as the perception of internal physiological changes, is implicated in many adult social affective processes, but its effects remain understudied in the context of parental socialization of children’s emotions. We hypothesized that what parents know about the interoceptive concomitants of emotions, or interoceptive knowledge (e.g., “my heart races when excited”), may be especially relevant in emotion socialization and in supporting children’s working models of emotions and the social world. We developed a measure of mothers’ interoceptive knowledge about their own emotions and examined its relation to children’s social affective outcomes relative to other socialization factors, including self‐reported parental behaviors, emotion beliefs, and knowledge of emotion‐relevant situations and nonverbal expressions. To assess these, mothers (N=201) completed structured interviews and questionnaires. A few months later, third‐grade teachers rated children’s social skills and emotion regulation observed in the classroom. Results indicated that mothers’ interoceptive knowledge about their own emotions was associated with children’s social affective skills (emotion regulation, social initiative, cooperation, self‐control), even after controlling for child gender and ethnicity, family income, maternal stress, and the above maternal socialization factors. Overall, findings suggest that mothers’ interoceptive knowledge may provide an additional, unique pathway by which children acquire social affective competence.