Bilingual infants vary in when, how, and how often they hear each of their languages. Variables such as the particular languages of exposure, the community context, the onset of exposure, the amount of exposure, and socioeconomic status are crucial for describing any bilingual infant sample. Parent report is an effective approach for gathering data about infants’ language experience. However, its quality is highly dependent on how information is elicited. This paper introduces a Multilingual Approach to Parent Language Estimates (MAPLE). MAPLE promotes best practices for using structured interviews to reliably elicit information from parents on bilingual infants’ language background, with an emphasis on the challenging task of quantifying infants’ relative exposure to each language. We discuss sensitive issues that must be navigated in this process, including diversity in family characteristics and cultural values. Finally, we identify six systematic effects that can impact parent report, and strategies for minimizing their influence.

Bilingual infants vary in when, how, and how often they hear each of their languages. Variables such as the particular languages of exposure, the community context, the onset of exposure, the amount of exposure, and socioeconomic status are crucial for describing any bilingual infant sample. Parent report is an effective approach for gathering data about infants’ language experience, however, its quality is highly dependent on how information is elicited. This paper introduces a Multilingual Approach to Parent Language Estimates (MAPLE). MAPLE promotes best practices for using structured interviews to reliably elicit information from parents on bilingual infants’ language background, with an emphasis on the challenging task of quantifying infants’ relative exposure to each language. We discuss sensitive issues that must be navigated in this process, including diversity in family characteristics and cultural values. Finally, we identify six systematic effects that can impact parent report, and strategies for minimizing their influence.

Data, materials, and code availability statement: All data and code used to create the results, tables and figures in this manuscript are available via the Open Science Framework at https://osf.io/psbxv/.

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Bilingual infants acquire languages in a variety of language environments. Some caregivers follow a one-person-one-language approach in an attempt to not ‘confuse’ their child. However, the central assumption that infants can keep track of what language a person speaks has not been tested. In two studies, we tested whether bilingual and monolingual 5-, 12- and 18-month-olds spontaneously form language-person associations. In both studies, infants were familiarized to a man and a woman, each speaking a different language, and tested on trials where they either spoke the same language or switched to a different language. In Study 1, infants only heard the speaker, and in Study 2 infants saw and heard the speaker. Bilinguals and monolinguals did not look longer to Switch compared to Same trials; thus, there was no evidence that infants form person-language associations spontaneously. This indicates that at least early in development, a central assumption of the one-person-one-language approach is not supported.