Tarvis, could you explain why? Other than the historical value, what makes it a poor firearm? The 13yo medium build son shouldn't have much of a problem with it. If he is taught how to use the sights and can use irons well...the rifle will be good enough out to 300y (400-500 take a bit more skill). The kick isn't hard, it will have the power needed for a 400+lb elk, and it is pretty much weather agnostic. His wife very well could be the same size as his 13yo son. I know several people that were doing cmp competitions with garands at that age. The biggest worry is weight of the arm, and that is a good thing here to an extent.
Tarvis, it also depends on what style of hunting they will be doing. Will they walk casually to the place where the elk graze most of the time, will they be actively stalking one elk all over the place, or will they be ambush (blind or stand) hunting? Each method brings with it it's own set of difficulties. If the child will be running all over the mountains, I agree, the garand is not ideal, but it will do. Most arms of a large enough caliber to use on elk at any distance will kick, so the garand's relatively light kick for the caliber while using full power loads (up to 2800fps with 170gr bullets) could be considered a good thing.
Once I get my reloading stuff, I will probably be using mine to hunt as well. I would recommend a .30-30, but I don't agree that it would have enough umph to humanely kill an elk.