The question of how home activities advance the early social and cognitive development of Latino children receives growing attention from psychologists and social scientists. Some scholars and practitioners, focused on promoting "school readiness," frame the problem as weak parenting, signaled by insufficient rich language or academic skills. Other theorists, rooted in ecocultural theory, argue that early socialization and cognitive engagement are culturally situated within routine home activities. These activity structures vary and change over time as families acculturate, adapting to local social ecologies. Little is known empirically about the activity structures within Latino homes, including how young children participate. We detail the social architecture and cognitive engagement pertaining to 6 prevalent home activities in which 24 Mexican American 4-year-olds were engaged over 14 months. We then report how children participate in these 6 activities, and their potential relevance to the cognitive skills gap seen at school entry. We found that children's activities reproduced heritage language, symbols, and knowledge less often than suggested in prior literature; children's typical level of cognitive engagement varied greatly among tasks; and the distribution of time spent in activities is associated with the mother's school attainment and home language.