Social skills and symbol skills are positively associated in middle childhood, but the relation between these domains is less clear in newly verbal toddlers. Vygotsky proposed that symbols are both tools for interaction and mental tools for thought. Do symbols help even very young children build skills for interacting with and conceptualizing the social world? Longitudinal data from 108 children and mothers were collected when children were 14, 24, and 36 months. Children's gestures and words during mother–child interactions were used as symbol skill indicators to predict children's abilities to engage others and the number of social-emotional concepts children portray during play. In a series of growth models, words had a stronger effect on engagement skills whereas early gesture use predicted later development of social-emotional concepts. Therefore, even in early development, symbols serve as both communication tools and mental tools to construct understanding of the social-emotional world.