I've got one of the Marlin Camp Carbines... they are fun little guns but the design isn't the best. I've replaced the disconnector twice and hammer once so far and I haven't shot many rounds in it.
The MAC on the other hand while a simple design, is robust and very under-rated. But, if the Tard doesn't like the MAC, I've always got the UZI, Mini UZI, MP5's, Colt SMG, MP-40, Sten or M-11 to choose from as well.
Mike