RTS games might be fun, but it might be kind of difficult to be fast and accurate with the touchscreen - hard to say without trying it.
Board games, as mentioned, will be both popular and fun. I have a 2 year old and look forward to teaching him checkers and eventually chess on something like the iPad - should be more interactive and interesting to a small child as well as less likely to put the pieces in his mouth.
I also think that there's something to be said about the inclusion of the digital compass in all models. Because that's currently a 3Gs only feature there's not a lot of games taking advantage of it, but that could change. Will be interesting to see if it's usable for an aiming or control mechanism of some sort in FPS or other games.
Lastly, I hope we see some educational games for small children (afore mentioned 2 year old). I'll likely have an Invisible Skin on the screen of the iPad and the whole thing in a case, so I will feel comfortable with him using it while sitting on my lap or on the table with me there (basically using it in a way which he can't drop it). Some matching games, and counting and learning letters type stuff will be really fun on something like this. If there isn't anything good out there I suppose it would be trivial enough to do a web based set of games.
EDIT: totally forgot that while I don't play tabletop RPGs anymore, the iPad would be an awesome way to extend that experience online. Speakers and mic for voice chat, large multitouch surface for virtual miniatures and maps... I would pay good money to GamesWorkshop for something like this, especially if it had an offline/single player mode and some cool precreated scenarios and league modes, etc. ****. I might have to finally learn Obj-C if they don't do this.
The iPhone was too small to make this a workable game genre, but a 10" should be plenty big.
