When I shopped for my first Canon body (30D), I skipped the Rebels in part because the small body felt flimsy and squished together, but that might be just the trick for small hands. I think if they're going to be mainly concentrating on composition (shooting in "Auto" or "P", for instance), there's nothing control-wise they'd miss in a Rebel, but I know that I really appreciated the extra buttons & dials on the 30D -- they make it so much easier to change settings, especially if you want to change two at once (one dial for A & one for T, for instance). That might be way beyond where your kids need to go, though.
The durability of the bigger bodies is nice, too. I drug my 40D up & down mountains for ten days in NM a couple years ago -- zero issues, though I never *actually* pounded tent stakes with it or anything.

I wound up letting my son use that camera for a semester for a photography class -- again, no problems, and he's been known to test the durability of things now and then. I still use the 40D as a backup. Obviously, I can't conclude that a Rebel would have been any less durable, but I've been very impressed with the 30D, 40D, and now 7D.
I don't know if this sounds ridiculous, but I'd consider hauling the kids down to a Best Buy and let them hold a Rebel and a 70D (or similar) to see if they seem intimidated by the larger, heavier body.
Anyway, note Dao's comment about EF lenses only on the 10D. I thought that had to be wrong, but it turns out the 10D was actually released before Canon started making EF-S lenses, so I'd give that some thought before popping for one of those.