Is this normal in language shift?

When I first got here, I thought I was seeing a textbook language shift situation. But I gradually realised something that I don't remember encountering mention of in my textbooks: there's a whole generation of fluent speakers here (most speakers under 25, actually) who only learned it in their early teen or preteen years. Most parents since the eighties speak only Arabic to their children, but the language is in wide use in situations like football games and farm work, and the younger ones seem to have picked it up there; in fact, it seems possible that the process is continuing with the even younger kids. Does anyone know of a similar case, or am I right in thinking this is a little unexpected?