FBF: you're right, it will certainly help the kids whose parents will give it up. What percentage I don't know. But it will definitely isolate the others all the more.
Another thing is that sometimes teenagers may be much more fanatic than their parents. This happens among JWs. I remember a Jewish family, pretty open at a time, which was lead into headstrong orthodoxy by the eldest son when he became 13 or 14 years old -- probably under fundamentalistic (Lubavitch) influence. The same happens in Muslim families: parents may have a reasonable or even liberal attitude with their religious practice, but their children themselves may find they are not taking it seriously enough. Nothing's simple!