Children learn the words of their native language(s) from interactions with their caregivers. Although previous research has found that the language children hear during those interactions predicts vocabulary outcomes, few studies have investigated how qualitative features of social interactions work together to affect children's vocabulary development, particularly for underresourced, language minoritized children. This study examined patterns of maternal interactive behaviors during toddlerhood in relation to children's later Spanish and English vocabulary development among 318 low-income, Mexican American families. Five maternal behaviors (acknowledging, elaborating, gaze, vocal appropriateness, and overriding) were coded from video recordings at age 24 months. At 36 and 54 months, child expressive vocabulary was assessed in both English and Spanish. Latent class analysis identified five distinct patterns of maternal interactive behaviors, which differentially supported or compromised child expressive language in English and Spanish. Implications of these findings for better understanding the role of caregiver interactions in dual language vocabulary development are discussed.