The number of bilingual speakers in modern society is on the rise, and they are characterized by numerous individual differences. Therefore, research increasingly examines various internal and external factors that could lead to these differences. Understanding their role in the acquisition of two languages is crucial for better comprehension of the course and outcomes of bilingual development. To enhance the understanding of early language development in bilingual toddlers, the aim of this study is to determine whether there is a correlation between internal and external factors and the lexical and grammatical development of bilingual toddlers acquiring Croatian and Italian. Parents of bilingual children aged 24 to 30 months completed a sociodemographic questionnaire created for this study, which collected data on the child's linguistic environment and language use. Additionally, they assessed their children's lexical and grammatical development using the Croatian scale Riječi i rečenice, which is part of the short version of the Communication Development Scales (Kuvač Kraljević et al., 2024), and the Italian version, Scheda Parole e Frasi - Forma breve (Caselli et al., 2015). The study included 27 participants from seven Italian kindergartens in the Istria County. Based on the literature reviewed, gender and birth order were selected as internal factors, while the language used by parents in communication, the language in which the child is read to, and the language whose proficiency parents consider more important were selected as external factors. Among the included factors, only reading in Croatian was found to be statistically significantly positively correlated with lexical and grammatical development in Croatian, with bilingual children who were read to in Croatian producing more words and longer utterances in Croatian.