Babies are aware of bilingualism from birth — if not before

Probably most of the world is bilingual, or more than bilingual. It is common in many countries to speak a national language alongside an international lingua franca such as Arabic, Spanish or English. On top of that, there may be a mother tongue that is not the same as a national language. A Nigerian, for instance, may be at once one of the million speakers of Berom, one of the 64 million speakers of Hausa and one of the 1.13 billion speakers of English. The same pattern is repeated across the globe.

In my experience, one of the best places to observe a wide variety of bilingual or multilingual individuals is Geneva, where a stable Francophone society is thickly overlaid with an international society, bringing their own mother tongues and the universally accepted lingua franca of English. In this setting, the linguistic grounding of children can be dauntingly complex. One friend, Italian by birth, has a child of five who switches between Italian, French and English, the syntactic structures still sometimes a little strange.