Purpose: This 2-phase study aims to extend research on parent report measures of children's productive vocabulary by investigating the development (n = 38) of the Spanish Vocabulary Extension and validity (n = 194) of the 100-item Spanish and English MacArthur-Bates Communicative Development Inventories Toddler Short Forms and Upward Extension (Fenson et al., 2000, 2007; Jackson-Maldonado, Marchman, & Fernald, 2013) and the Spanish Vocabulary Extension for use with parents from low-income homes and their 24- to 48-month-old Spanish-English bilingual children. Method: Study participants were drawn from Early Head Start and Head Start collaborative programs in the Northeastern United States in which English was the primary language used in the classroom. All families reported Spanish or Spanish-English as their home language(s). The MacArthur Communicative Development Inventories as well as the researcher-designed Spanish Vocabulary Extension were used as measures of children's English and Spanish productive vocabularies. Results: Findings revealed the forms' concurrent and discriminant validity, on the basis of standardized measures of vocabulary, as measures of productive vocabulary for this growing bilingual population. Conclusion: These findings suggest that parent reports, including our researcher-designed form, represent a valid, cost-effective mechanism for vocabulary monitoring purposes in early childhood education settings.