Debate. Children are never too young to learn rhetoric!
LOL
How about adult level card games? You make have to make some modification to account for small hands: for example our kids were playing Canasta (when other kids their age were playing "go fish" and "war") and they used an extra chair tucked under the table to spread out the cards that would have been held in their hands (you can accumulate lots of cards in your hand in this game and they simply couldn't hold them all). Canasta is great for strategic thinking and math skills, among other things.
Origami is another good activity - it works fine motor, sequential and visual spatial skills. My daughter was obsessed for awhile and our house was filled with her creations
