my son is just turning four and has been playing with the little legos for the last half a year. He's really into the "Knights" right now-Vladeck and Rascus. In fact we went to lego land the other day and it was great- no teens and better food and lines than disney.

He also really likes nature books; he gets the magazine My Big Backyard. A backyard sandbox is always fun as are binoculars.

Take him to a demolition derby. My son saw his first at 2 and plays demo derby with his cars everyday.