I found an interesting article on the BBC News website about Asian languages in the UK which discusses how some UK families of South Asian origin are trying to encourage their children to continue speaking their native languages, such as Bengali, Urdu, Punjabi and Gujarati. The children are taught in English at school, but some also attend complementary and weekend schools run by local communities where they are taught in their native languages. Such schools are run by volunteers and receive no government funding, and are helping to maintain bilingualism among their pupils, and perhaps because of this, those pupils are also achieving good results in their mainstream schools.
It seems to be common among immigrant families that native languages last only two or three generations, unless community efforts are made to maintain their languages. The situation can be similar for minority languages such as Maori and Irish. Another article I came across today is not very hopeful about the future of the Maori language and predicts it will die out in 50 years or so. In spite of initiatives to promote the language, the young generation is increasingly turning to English, even those who attend the Maori-medium schools. In the schools they speak Maori, but elsewhere many speak only English.