International adoptions count for 40,000 children each year.

Most of them are adopted by families from North America and Western Europe.

These events provide the researchers the opportunity for experimenting how language development takes place.

Even if most are under three years, thousands are older children which typically lose their mother tongue rapidly and learn fluently their new language.

A team at Harvard University investigated these older children to assess how infants learn their native language. As a first step, babies pronounce one word at a time, mostly nouns ("ball") or social words ("hi").

Growing older, they develop longer and more complex sentences, including verbs ("take") and grammatical words ("about"). "These changes in the infant speech could be due to the child's increased cognitive abilities or, as Snedeker asserts, they might also simply be side effects of the learning process itself and independent of the child's age or cognitive abilities", said Jesse Snedeker, one of the researchers.

Nouns are easier to learn, because they can depict non-abstract notions, which can be watched. The team checked the way Chinese adopted children - aged between 2 ½ and 6 - learnt English. The progress of these children was followed and compared with that of children learning English as a first language, from their first year in the U.S.

This comparison is very important as language development is often out of sync with their cognitive development and maturation.

Unlike most second language learners, the Chinese adopted children have no dictionaries to consult or to translate what they hear, that's why the process is similar to learning their first language: they find the meanings of words by associating it with what happens around them. There is one difference: as they grow older, their cognitive ability is higher.

But the steps they took in learning the new language were the same: nouns and - after a period - verbs. Like babies, the preschoolers first pronounced one word sentences, followed by short telegraphic sentences ("Mommy eat").

But these adopted children passed through these steps more rapidly than the infants, a sign that they can catch up their peers born in an English-speaking environment.

Older and more mature, children go through these same steps when they learn a new language via immersion in speech.