For all children, language acquisition begins at birth as babies start recognizing the sounds of their native language(s). Pediatric milestone evaluations include assessing timely language development, with the most simplified version of grammar and lexical acquisition assessments as two-word sentences at age two and three-word sentences at three. More robust measurements of language development are utilized in developmental delay clinical follow-ups and linguistics studies.
Language acquisition is one measure of cognitive function as its progression is an important component for effective communication and learning. Severe language delays or persistent deficits may cause significant impacts and be considered a disability when they interfere with daily functioning. Researchers recommend supporting language acquisition through rich verbal and social contexts, especially when children are learning more than one language. Bilingualism presents an added challenge to evaluating language acquisition and in the framework of other conditions linked to developmental delays such as autism, assessing language milestones may require more refined screening methods.
Language Acquisition in Bilinguals
Simultaneous dual language acquisition presents additional challenges for young children. Simultaneous bilingualism is differentiated from second language acquisition, where the first is defined as early enough exposure to two languages to be considered as learned together. However, there is no clear consensus on the age at which learning another language is considered a second language (L2). There is no set age cut-off for bilingual exposure, but literature review shows 2-3 years old as the latest age by which children are considered simultaneous dual language learners. This age is determined by their outward demonstration of an awareness for dual-language usage. Introduction of an L2 after that age is generally considered second language learning.
For bilingual development, there are two main models in linguistic research: the unitary language system hypothesis and dual language system hypothesis. The unitary language system hypothesis emphasizes the funneling of input from both language into one linguistic system, where one set of grammatical rules are applied to both languages in the initial stage of language learning for bilingual children. The languages separate into two linguistic systems at around age 3, much like their bilingual adult counterparts. In contrast, the dual language system hypothesis presents bilingualism as a process established as early as at birth into two separate linguistic systems, and this is the dominant model currently supported by research. Research has shown infants’ ability to distinguish between both languages through studies on phonology and grammar. However, this establishment of separate systems does not exclude cross-linguistic influences. Young dual-language learners transfer rules of one language to the other in their early years, and by elementary school will be better at distinguishing those rulesets.