We know that young children acquire language through everyday interactions. But little is known empirically about the salience and influence of parents' beliefs and explicit strategies, relative to tacit language socialization, especially among parents who consider bilingual language development. This thesis digs deeply into three contrasting Mexican American households to observe the extent to which mothers articulate language goals and beliefs, and then act from them. Parents' beliefs about how languages are learned influence their young children's first and second language development by parents' management of family routines, daily activities, and language practices. Parents' language learning beliefs emerge from understandings they have of their past language experiences and their response to the current environment where their children are growing. Parents express their language learning beliefs in relationship to language practices that occur within the context of their family, community life, and their children's schools. The basic components of Language Policy Theory--beliefs, practices, and management--are useful when considering the importance of parents' influence over their children's first and second language learning, but language policy also must be theorized in the local contexts where children are growing and learning. Ecocultural Theory is useful in situating Language Policy Theory in the historical, cultural, and environmental context where bilingual parenting occurs in order to understand how parental language learning beliefs, coupled with family routines and daily activity choices, influence the language learning opportunities of young children. This thesis presents findings of case studies of three first-generation Mexican American mothers and their young children who participated in a twenty-four family ethnographic study of child-rearing practices in Mexican heritage families. From the twenty-four mothers in the initial study who were the primary care-givers for their pre-kindergarten age child, emic parental beliefs about language development, childhood bilingualism, and features of the local environment emerged. In response to the local context, the mothers consciously served as facilitators, teachers, or role models for their children's bilingual development through their explicit practices. In case studies, mothers expressed and exemplified variation in bilingual parenting intentions with one mother seeing herself as learning to be bilingual from her children, another mother learning to be bilingual with her children, and another mother explicitly teaching her children to be bilingual. Parental language learning beliefs, family language practices, and parents' management of children's daily activities have implications for children attaining the language learning goals which their parents have for them and also have implications for teachers of second language learners.