We examined the influence of children's peer relationships and maternal emotional socialization on children's development of emotion knowledge. Children's emotion knowledge was assessed at the beginning (time 1) and end (time 2) of their first semester of kindergarten. Children's peer interactions were measured through observations and teacher ratings. Mothers' beliefs about teaching emotion language and emotional expressive styles were assessed through questionnaires. Children with more stable friendships demonstrated greater increases in emotion label knowledge between time 1 and 2. More popular children had greater increases in emotion script knowledge between time 1 and 2, as did children whose mothers believed in teaching emotion language. Results have implications for future research regarding parents' and teachers' beliefs about socializing children's emotional development.