Can't you lock down the entire itunes store?
It isn't as if your kids can't find naughty words elsewhere on the internet.
Even if you couldn't lock down the iTunes store its the parents responsibility to... parent, not Apple's.
I think this has less to do with censorship and more to do with potential loss of revenue from iTunes.
You must not follow Trent Reznor too closely, he basically gave away his last 2 albums.