This study investigated the relationship among home language use, parents' beliefs about dual language development, and Spanish-speaking children's vocabulary knowledge. Parents (n = 162) completed a questionnaire about their home language use and beliefs about dual language development, and elementary-age children (N = 190) -- Kindergarten (M[subscript age] = 5.71, SD = 0.56), second grade (M[subscript age] = 7.52, SD = 0.31), and fourth grade (M[subscript age] = 9.35, SD = 0.45) -- completed conceptually-scored vocabulary assessments. Principal component analyses revealed that Spanish-speaking parents' beliefs about dual language development are heterogeneous. Further, parents' beliefs can be characterized differently according to their children's English proficiency designations and grade levels. Structural equation modeling analyses revealed that the "Bilingual Facility" parental belief factor was associated with home language use practices, which in turn were associated with children's vocabulary. However, this association only applied to limited English proficient students and their parents. These results underscore the importance of attending to Spanish-speaking parents' beliefs, as they appear to relate to home language use practices and, importantly, they also relate to their children's vocabulary achievement.