Restrict Content in iTunes
This used to be possible, but with the latest iteration of iTunes, it doesn't work.

The method was always as described above, and the same thing happened on the last major release of iTunes.  Apple eventually seemed to put things right, but it's happened again this time round.

I have movies stored on my Mac and Home share them via iTunes.  When my daughter accessed movies on her Mac, which had parental controls set in iTunes, anything over 12 (UK rating) was greyed out and unable to be played.  Now they're all accessible.

Perhaps Apple will resolve this issue too, if enough of us report it.