I got my R back!
After leaving Joe alone for a couple of minutes with my laptop (not a good idea, by the way) chanting "Keys, keys..." over and over, I looked over and saw that he'd pried up a sizeable chunk of the keyboard: 17 keys, including the oddball Enter, Shift, and Space, as well as all of the arrow keys and the right Alt.
As First Responder, I kept the situation from further deteriorating by banishing the offender to the kitchen. Plus that way he couldn't see me laugh while I was trying to yell at him.
The keys were in varying stages of disassembly, so by a little observation, I finally figured out how the little white things hook together with each other, the plane of the keyboard, and the key caps. I should probably write it up in a how-to (complete with preventative steps; e.g. "Two-year-olds and laptop keyboards don't mix") so future hapless souls can attain at least some measure of hap.
Anyway, by the end of putting the 17 keys (f,./;'\) back on, I was getting pretty confident in my abilities, and I ran upstairs to fetch my long-detached R key (at least since XP/Agile Universe in August). Alas, only the inner white plastic thingie (don't ask) was still with it. What to do?
Well, truth be told, I don't use right Alt that much, so I swiped its outer thingie, hooked it into R's spot, and presto! I now have a keyboard with a missing right Alt, instead of a missing R. A big improvement (though possibly not for Dvorak).
Now all I need to do is put all the mounting screws back in and find a new outer thingie, and the keyboard will be as good as new.
Well, once I clean out all the hair, fuzz, and gunk that I didn't have the patience to take on this time around. Of course, there won't be a next time, because a certain little someone has lost all his laptop privilages.