The developmental experiences of very young American Indian children today are not well documented in the current literature. The present study sought to explore the social-emotional development of American Indian toddlers living on a Northern Plains reservation, as a function of maternal variables. Mothers completed self-report questionnaires about their experiences and their children's development. Observer ratings of children's development also were conducted. Maternal stress, substance use/abuse, perceptions of stress in the mother–child relationship, social support, and American Indian cultural identity were significantly related to children's social-emotional development. This study is the first to explore these relationships in a Northern Plains American Indian sample of young children and their mothers. Results suggest possible points of intervention for improving the developmental outcomes of very young American Indian children.