Juliette, a two-and-a-half-year-old French-English bilingual, was playing with Marc, a five-year-old English-speaking boy. Their usual language of communication was English, but to please and surprise her, Marc decided to speak to her in French. He asked his mother for the equivalent of "come" in French and then returned to Juliette and said, "Viens, viens." Much to his surprise, Juliette was far from pleased; instead of smiling, she said angrily, "Don't do that, Marc," and repeated this several times.
Through her reaction, Juliette was showing the importance of the person-language bond that exists between bilinguals, be they adults or children. In an earlier post on language choice, we noted that bilinguals often have an agreed upon language they customarily use with bilinguals they know well. Violation of this "agreement" is likely to create an unnatural or even embarrassing situation, which may end with the question, "Why are you speaking language X to me?"
As a bilingual friend once told me, "I never speak English to my French friends, even if they are fluent in English. I find it unnatural, and I hate it when close friends suggest I speak to them in English ....."
Of course, if a third person enters the room, or if the location of the interaction changes, or the participants want to exclude someone, speaking the other language is considered perfectly natural. But as soon as the situation permits it, the participants will revert to their customary language of interaction. This does not exclude bringing the other language into the interaction for a word, a phrase or a sentence (see the post on the intermingling of languages), but the base language is usually firmly established.
Sometimes, the agreed upon language is changed for good and this may create some distress. Concert pianist Kenneth van Barthold told me how as a boy he would speak Dutch to his mother. Over dinner one evening, at the onset of World War II, his British father announced that since there was a war on, and consequently they could not have any further contact with The Netherlands, the language of the family was henceforth to be English! His mother burst into tears and left the room. Kenneth van Barthold reassured me that he continued speaking Dutch to his mother until he was an adult ..... but he most probably did so in the absence of his father.
The person-language bond is particularly strong in very young bilingual children. Juliette's reaction above is not unique. Here is another example. Little Luca, bilingual in French and Croatian, was speaking to his paternal grandmother. Their language of communication is French but since they were in Croatia, his grandmother asked him to name a few things in Croatian. He refused to do so and then said, in French, "It's mummy who asks that" (Luca speaks Croatian only to his mother and her parents). Luca's reaction was in fact rather mild compared to that of other children who can get quite upset when the wrong language is used.
Psycholinguists have asked themselves why the person-language bond is so strong in very young bilinguals. Some have proposed that it helps them differentiate their languages. In order to do so, young bilingual children rely on different factors: the phonetic and prosodic cues (e.g. the rhythm) of each language, other structural aspects, the context the language is used in, and, very importantly, the language spoken by a given person.
As a consequence of this bond, bilingual children are often ready to correct and help out the adult. For example, when Juliette's mother switched over to English, little Juliette translated what she said into French, the language they always spoke together, thus reestablishing the person-language bond. Only when her mother failed to understand something her daughter was telling her in French did Juliette agree to use English, but she switched back to French as soon as possible.
So the next time a very young bilingual child refuses to speak to you in a language you don't usually use with her, don't be surprised. She is simply busy acquiring and differentiating her languages as well as working out the social constraints of language choice.
Reference: "Acquiring two languages". Chapter 15 of Grosjean, François (2010). Bilingual: Life and Reality. Cambridge, Mass: Harvard University Press.
"Life as a bilingual" posts by content area: http://www.francoisgrosjean.ch/blog_en.html
François Grosjean's website: www.francoisgrosjean.ch