Immersion programs have long been considered the gold standard for school-based language revitalization, but surprisingly little attention has been paid to the quantity and quality of the input that they provide to young language learners. Drawing on new data from three such programs (Kaqchikel, Western Subanon, and Māori), each with its own particular motivation, objectives, and pedagogical practices, we examine a key component of this revitalization strategy, namely the amount and type of lexical input that children receive. Our findings include previously unknown facts about the number of words that children in these programs hear per hour, the ratio of word tokens to word types, and the skewed frequency distribution of the particular words that make up the input. We discuss our findings with reference both to comparable measures for first language acquisition in a home setting and to their relevance for pedagogical strategies in the classroom.