Child-level factors associated with Spanish-English bilingual toddlers' productive vocabulary growth

This longitudinal study-conducted in the Midwestern United States-examines the child-level factors that promote Spanish-English bilingual toddlers' (n = 47; M_age = 18.80 months; SD_age = 0.57) productive vocabulary skills from 18 to 30 months of age. At 6-month intervals, caregivers reported on toddlers' Spanish and English words produced as well as their language exposure at home. Video recordings at child age 18 months yielded estimates of toddlers' speech output (word tokens per minute). In addition, at child age 18 months, caregivers reported on toddlers' linguistic skills (comprehension), demographic background (gender, household income), and nonverbal behaviors (gesture production). Results showed that toddlers were exposed to both English and Spanish and received more Spanish than English from primary caregivers; there were no significant primary caregiver input differences across time. Growth modeling revealed linear growth rates for Spanish and conceptual (Spanish, English combined) vocabulary and a curvilinear trajectory for English vocabulary. Furthermore, toddlers' Spanish and conceptual vocabularies were positively associated with their higher frequencies of token use, greater production of gesture, and greater comprehension skills, even after controlling for input. Moreover, Spanish and conceptual growth rates were positively associated with higher token use. In terms of English, toddlers' vocabulary at child age 18 months was positively associated with their comprehension skills. Toddlers' use of more gestures and tokens as well as gender (boys) influenced their English acceleration rates over time. Findings indicate that unique trajectories exist for each of a bilingual's languages and these trajectories are differentially influenced by child-level factors, including their speech output, not only exposure to language. (PsycInfo Database Record (c) 2024 APA, all rights reserved).