The girls normally use my old G4 (their monitor is out of the picture), complete with £5 keyboards that are easy to replace sans spills. In fact I just bought them this, which takes a bit of getting used to, but it can cope with mango juice, yoghurt and even cola.
Unfortunately it looks like the G4 motherboard has gone belly up, so at present I'm lucky to get access to my own computer.
So, maclick, why do you put your computer under the desk? Isn't it an inconvenience to have to reach under there to plug in devices or insert CD's? Looks like you have room on the top, so there must be some reason you like it that way. (Just wondering.)