Many parents would like their children to grow up speaking two or more languages. If each parent is a native speaker of a different language and they speak those languages to the children, the children will acquire both languages. This is called the one parent one language method (OPOL).
In other families the parents may share the same native languages and speak other languages fluently as well. They could try speaking their foreign languages to the children at certain times or on certain days, but this can be difficult to stick to.
The language situations within families, and in the communities in which they live, differ quite a lot, so the arrangements for raising children bilingually need to be taylored to the circumstances, and quite a bit of flexibility may be necessary. If parents stick rigedly to one particular arrangement, the children might refuse to cooperate, and this can be a source of friction within the family.
If a family lives in a community where one language is spoken, but speak another at home, the children might refuse to speak the home language once they realise that nobody outside their home speaks it. This is especially a problem with minority languages that aren’t widely spoken. However the children might be more willing to use the home language if they have regular contact with other people who speak it, such as relatives, or if the family makes visits another country or region where the home language is spoken.
Fortunately there’s plenty of advice available online, and quite a few parents write blogs about their experiences with bilingual child raising.