Do children hearing two languages acquire language at a slower rate?

It is often assumed that children who are exposed to two languages from birth will acquire language at a slower rate compared to children who only hear one language. But is there any evidence to confirm that this is actually the case?

Annick de Houwer, Marc Bornstein and Diane Putnick have investigated this topic and have compared the comprehension and production vocabularies of bilingual and monolingual children in their second year of life. They collected data for 31 middle-class bilingual children with Dutch and French input from birth and 30 children from similar backgrounds with only Dutch input from birth. In the bilingual families, all but one family reported that they used the “one person, one language” principle of speaking to the child and that this language pattern started from birth. In 14 of the bilingual families, the mothers spoke Dutch and the fathers spoke French to the child and in 16 families, the mothers spoke French and the fathers spoke Dutch to the child; in all cases both parents knew Dutch and French. Children in the monolingual group heard just Dutch, spoken to them by their parents and other caregivers from birth.  The children were studied at ages 13 months and again at 20 months using research methods that allowed the researchers to examine the children’s vocabulary sizes for both word comprehension and word production.

The comprehension results showed that at 13 months old, the bilingual infants understood as many Dutch words as the monolingual infants. However, the overall word comprehension for the bilinguals (i.e. Dutch and French combined) showed that, on average, the bilinguals understood 71% more words than the monolinguals, a significant difference. At age 20 months, the children were only compared for their Dutch comprehension and the results showed that the monolingual children understood similar numbers of Dutch words as the bilingual children.

As one might expect, the number of words actually produced at age 13 months was low for both the monolingual and bilingual children but nevertheless the number was similar for each group, regardless of whether the words were Dutch only or whether they were French and Dutch combined. The researchers also point out that there was a lot of variation between the individual children in the number of words that each child could produce. When the researchers compared the children at 20 months, they again found that, on average, the bilinguals produced similar numbers of words as the monolinguals, although again there was a great of interindividual variation.

In sum, these separate measures of comprehension and production show that there were no bilingual-monolingual differences for Dutch at ages 13 or 20 months. There was, however, one difference; when the bilinguals’ languages were combined at 13 months, the bilinguals outperformed the monolinguals in terms of word comprehension. The results of the study support the researchers' conclusions that exposing children to two languages from birth does not slow down lexical development. Some of the bilingual children in their study understood and produced more words than some of the best performing monolinguals. The researchers argue that if a bilingual child is showing signs of slow lexical development then parents and speech professionals should try to understand what is causing the delay rather than attribute it to bilingualism.

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Houwer, A., Bornstein, M. and Putnick, D. (2013). A bilingual-monolingual comparison of young children’s vocabulary size: Evidence from comprehension and production. Applied Psycholinguistics, 1-23.

Doi: 10.1017/S0142716412000744

This summary was written by Sue Fox