How to keep the minority language?

In Brussels you can probably find any language you want. It is crazy when instead of greeting serving personnel asks „Nederlands? English? Francais?“ In case our native language is not one of these, how do we keep it and make sure that our children know this language very well? I will call this language the minority language – language which is different from the main environment’s language.
After reading a book* on this, I think I understand the main principles. The main main principles are actually two:
Exposure. The basics for learning language is of course exposure. Babies and small children who are exposed to certain language quite quickly learn it. In general, to become fluent in the minority language a child needs at least 25 hours of exposure per week. This is why children whose only one parent speaks the minority language are much less successful in mastering it than children whose both parents speak the language. Both parents speaking the same minority language means more exposure to this language.
Need. A child must feel the need to speak the minority language. Children are practical – if they see that their mom actually understands and can talk in Dutch, why would they bother to talk to her in Hungarian, for example? Often times the need is right there. If a child enjoys spending time with his Latvian-speaking cousins, he of course has to speak in Latvian. Sometimes the need can be created or modified. The author of the book writes that for a long time he tried to somehow hide that he knows Japanese but kept using English. If the movie is in Spanish (although it actually exists in another language), a child has to understand this language to enjoy the movie.
Books, books, books. They are excellent resources. Even the number of books in the house influences how well children speak, they say. I could maybe argue with that, but the presence of good quality books does encourage kids to learn language. Reading aloud a book with kids, even when they know how to read themselves, contributes to their language knowledge. Because written language is always richer than spoken word.
I got some good ideas and cannot wait to implement them. When children already know how to read, we can leave some short phrases in the minority language on the wall in the bathroom, for example. Children will enjoy reading it. Or we can put a paper with some phrase in their lunchbox to school. In this way children practice their language even when parents are not there. Or if you travel a lot and miss time with your kids, record a video of you talking in the minority language or reading some book in the minority language. Another idea could be introducing and maintaining some homework routine in the minority language. I doubt this a little bit because mostly children are not motivated at all, and if they are not motivated, not much good will turn out. But if children agree, it is also an idea to try.
When children start to attend a majority language school, it swallows as a tsunami: the majority language becomes so prevalent and the minority language finds its place somewhere in the corner. So the best time to teach the basics of the minority language is before school. Otherwise it is so difficult to go against the influence of the school.
How do you make sure your kids learn your language?
*Adam Beck (2016). Maximize Your Child’s Bilingual Ability