In this chapter, we describe aspects of music processing in three phases of childhood: infancy (0 to 2 years), the preschool period (2 to 5 years), and the primary school years (6 to 10 years of age). In each developmental phase, we depict age-related changes in music cognition and the ecology of children’s musical lives—facets that contribute to socialization in family and community and to the acquisition of culture-specific musical knowledge and skill. Multimodality and social contexts are the hallmarks of children’s everyday musical experiences. Insights from laboratory research, which are based largely on Western, middle-class populations, reveal the abilities of very young infants and the subsequent acquisition of implicit and explicit musical knowledge. Systematic musical exposure or training is presumed to have more potent effects in earlier than in later developmental periods. We conclude with a suggestion of further lines of research that could enhance our understanding of musical development.