This longitudinal investigation focused on the language and literacy environments of 1046 children from low-income families across children's first three years of life. Children's language and cognitive abilities at 14, 24, and 36 months of age were examined in relation to the frequency of children's participation in literacy activities, the quality of mothers' engagements with their children, and the provision of age-appropriate learning materials. Each aspect of the literacy environment uniquely contributed to the prediction of children's language and cognitive skills at each age, beyond child and family characteristics. Similarly, literacy experiences at each of the three ages explained unique variance in children's 36-month language and cognitive skills. These findings point to the importance of targeting multiple aspects of the literacy environment, already by the first year of life, as a means to supporting the development of young children from low-income families. (Contains 7 tables.)