Defining bilingualism in infancy and toddlerhood: A scoping review

Aims and objectives: The aim of this manuscript is to provide an overview of the population and languages studied and the methods and practices surrounding the definition of bilingualism in children below age 3. Methodology: A quantitative descriptive scoping review Data and analysis: From 530 articles, we identified 127 papers (167 studies) that met our predefined criteria, of which 144 studies defined their bilingual population. Findings/conclusions: The samples investigated were predominantly western in geographical origin and languages. Percent exposure was the most common method to measure bilingualism among infants and young children, with 20% and 25% the most used cutoffs as the minimum requirement for children's second language. We also analyzed the predictive value of these cutoffs on the likelihood that studies reported a significant difference between monolinguals and bilinguals. The stricter the inclusion requirement for bilinguals was, the higher the odds of a study to report a difference between monolingual and bilingual children. We conclude that a lack of uniformity of definition in the field may be one factor that predicts whether or not significant differences are reported. Originality: This scoping review provides developmental researchers with a unique overview of the different practices used in the field to characterize bilingual and monolingual infants/toddlers. The reported results can be used as preliminary evidence for the field to report and carefully formulate how to categorize monolinguals and bilingual infants. Significance/implications: As globalization continues to foster migration and intercultural exchange, it is essential for developmental researchers to diversify their samples and language groups. We highly encourage researchers to carefully document the definitions and rationale for all their language groups and to consider analyzing the impact of bilingualism both from a categorical and continuous approach.