In some areas of the world bilingualism is quite common. I'm bilingual myself and I'm also quite high on the English proficiency scale. My kids will probably grow up to be at least trilingual. Of course it's hard to say, but I intend to speak West Frisian with my kids, my girlfriend and her family will talk in Bulgarian to them. We communicate in English with each other and depending on the country where we live by the time, they will also learn that language. To say that they will become truly bilingual or trilingual (or quadrilingual) is quite a stretch, but they will take in at least something.