I think it's just a case of the kids' parents not listening to the music.
If the parents are playing it, the kids will hear it. Growing up, my
first exposure to non-pop music was the soundtracks of musicals at the
time. My father played "My Fair Lady," "The King and I," and "Brigadoon
so often that, without really sitting down and listening to them, I got
to know each score by heart.
It also depends on what the kids friends are listening to, but not always.
My father was a big fan of Mario Lanza and played his music a lot. When
I mentioned the singers name to my best friend, he thought I said "Mary