I don't get why someone would not try to change the cycle...if people you know got knocked up at 15 and had a [censored] life thereafter...then wouldn't it make sense to say "hey, y'know, let's not start having sex at 13 or 14" and avoid the whole deal? That'd be like watching several of your friends each pick up a gun, point it at their face, pull the trigger, and die...and then picking up a gun, pointing it at your face, and pulling the trigger...
Does it honestly not occur to them to not do it? Do they really not know what causes pregnancy? Is it some sort of weird self-esteem thing?