Configure iTunes to support multiple users on one mac

I have a nice 2009 mac OSX that my two boys share. They have their own accounts on the computer and their own iTunes accounts. They want to be able to authorise the computer to play the stuff they buy in iTunes and synch it to their devices. Right now they have to re-authorise every time they log in and other indignities.

Any suggestions for making this work smoothly would be appreciated.