I restored my iTunes folder from a Time Machine backup (due to my kids deleting some playlists, which I wanted to recover).
Don't let them mess with your computer account at all.
Create their own computer login as a regular user, not admin and let them mess up their own stuff.
Chris, thanks for that suggestion. I would still like for my kids to access my iTunes music, but just don't want them to mess with the playlists etc.
If I set up another account, then follow the instructions here -> http://support.apple.com/kb/HT1203
... to share the library with them, I'm guessing that they could still make changes to the playlists etc? (it doesn't specify in that article.)
I had the same issue, but wasn't able to delete the itdb files. The answer was that they were "in use".
So I renamed them, relaunched iTunes and voila... my itunes was back!
Still have not been able to delete the old itdb files though, but will try again after rebooting everything as I have my whole itunes library on a NAS server