I set up an old PC with Edubuntu 12.04 for my girls, with an admin account for myself and normal user accounts for both of them. Unfortunately, they are not able to shut down the computer by themselves with this configuration. Choosing shutdown from the (Unity) panel menu will log them out, but that's it. How do I give them shutdown privileges?

Please note that they are 5 and 7 years old and just starting to find their way around a computer. Solutions that would require them to open a terminal and sudo whatever are not helpful -- and I don't want them to be able to sudo anything, anyway. I need the panel menu entry "Shutdown" to work for them.