I guess it depends on how you raise your kids. I have three of 'em (14,13,11) and they are well-versed in all sorts of music, I've always encouraged them to listen to whatever piques their interest. My CD collection is theirs to experiment with so long as they treat the discs properly and return them when they're done listening (different rules with my vinyl, I'll cue it up and listen with them but they are not allowed to touch my Oracle 'table). When each child reached the ripe age of 10 I bought them their own stereo for their room (click on my System to see the modest systems) to encourage them to make music part of their daily life.
I recently bought them MP3 players so they can enjoy tunes when they're out and about, Creative and Apple make inexpensive players the kids love.
In addition all three of 'em are in the school band (flute, oboe) as well as taking their regular music classes in school. I heard my son's band recently, they covered some interesting material that included Bach, swing, and some light jazz. We listened to Steely Dan and some rap in the car on the way home *L* It's up to the parents to nudge their kids into music rather than leaving it to the kids to waste all their time watching tv, playing video games, and chatting on the internet.