This Guide is specifically intended for staff in Migrant and Seasonal Head Start (MSHS) programs, which are funded to provide comprehensive child development services to the children of migrant farm workers from birth through compulsory school age. The authors attempt to navigate the research on first and second language acquisition and development on infants and toddlers, consistent with the Head Start definition of "infants," (i.e., children younger than 36 months of age) (ACF, 1996). They also identify and attempt to respond to key questions and concerns obtained from MSHS program staff. At its core, this Guide aims to integrate information about children's developmental progress in acquiring one or more languages in infancy with practical considerations of how adult caregivers can best support that development. The author's aim is to produce as practical and as meaningful a resource as possible. Bilingual Infant/Toddler Environments (BI/TE) MSHS Program Questionnaire is appended.