Raising children in a multilingual family
Working with children who live in bi- or multilingual homes has been something new for me, and different families have different needs, philosophies and approaches to deal with this.
In one family I know, Mum speaks German and English, Dad speaks Serbian, and the child speaks all three languages. His language at school is German (and, of course, Swiss German). Every night over dinner, the family speaks a different language. Monday might be Serbian, Tuesday German, Wednesday English, and so on.
In our family, English is the only language spoken at home, while both children speak German and Swiss German during their school day.
There is a lot of research out there about how children "code-switch" between language contexts: that is, a child might associate one place (like school) with one language, and another (home) with the other, and learn to slip easily between languages as they go from one place to the other. It becomes second nature.
That can be problematic when a child has to speak that language out of context. My daughter gets annoyed when she has to speak German at home, for example, to make a phone call or talk to a neighbour. For her, German is for school and English is for home -- which is why they refuse to help me practise! Interestingly, one of the developmental ways bi- or multilingual children differ cognitively is that they learn to "triage" what they hear and almost instantly identify the language to respond in.
Another family speaks Polish, German and English. I see them every week for English practice, and they speak German and English at their bilingual preschool. One parent also speaks to them in Polish, and the children understand and reply in English. They value English but, of course, want to maintain ties to Poland. As a result, they are trying to find a balance between the practical (English) and the emotional (Polish), while in a German-speaking country.
There's no perfect way to maintain a child's multilingualism.
A parent might ask, "Should I speak English to my child all the time?" The answer is no. There's no absolute advantage to speaking purely one language to your child, especially if you're not fully fluent yourself. Provided they are getting regular exposure to English in a variety of ways, that's enough. And you want to be able to express yourself fully to your child, of course!
Here's a great link with more detail and suggestions for multilingual families from the Speech Language Literacy Lab (SL3) in the USA.