It sounds like you made the same mistake that I did. You have two IDs! Worse is the fact that apparently some apps were obtained on one ID and some were obtained on the other.
Be forewarned that it's not possible to combine IDs and it's not possible to transfer purchases from one ID to another ID. Whenever you need to update apps obtained with the "wrong" ID, you'll need to log out and back in again. Alternately, your kids can do it from the iPods without the hassle of logging out/in BUT thay'll still need the password.
In my case, one ID was "firstname.lastname@example.org" and the other was "first last"
I changed the second to "email@example.com" and I made both passwords identical. This way I always know exactly which one I'm using but I can easily and quickly switch back and forth.