...from a NAS device. Like you, I've spent HOURS getting all the TV cataloged, named correctly, and with images. Like you, I have kids I don't want watching certain things and I solve it thusly:
1:Create a share on your NAS which has the items you DON'T want them to watch and make it so that it needs a password or whatever credentials you need to connect to it.
2:Add the share to XBMC, but put it under a Master Profile.
3: Create another Profile for your younglings that can't access the shared files. Double bonus, since you password protected the share, if they do go scanning the network, they'll have to have to know the (hopefully) different password to mount the share with your non-kid content.
4:??? Profit?
Check this out:
http://forum.xbmc.org/showthread.php?tid=108232 I think it will help you sort your media out with haste.