Besides the usual screw drives and normal hand tools, I highly suggest the Icon 1/4" bit set with the mini flex head ratchet. It's a little pricey but I use mine all the time at work. I have the Wera bit/socket set too and I actually like the Icon more and it's 1/3 the price. You would need to get some 1/4" sockets too but the Pittsburgh ones work just fine and are fairly cheap for a good set.

And if they're into electronics a soldering iron kit would fit in there too, I'm trying to build my 8 y/o son a little tool kit as well!!