ADD runs in our family ("in fact, it practically stampedes"), and I'm starting to see my toddler's attention become more and more difficult for him to control; he's beginning to have difficulty maintaining focus in the face of mild distraction even to get something he desperately wants.

I know that children's brains are surprisingly elastic and that things like attention and impulse-control must be learned, and must be learned at an early age. So I'd like to give the boy as much of a advantage as he can get in the face of heredity.

Are there any well-defined exercise or activities that have been shown to increase a child's (ca. 3 to 5 years old) ability to resist distraction and increase impulse control?

N.B.: I'm not looking for general advice ("make sure he gets plenty of rest") or things to avoid ("turn off the television"), I'm looking for activities and games to play that will actually help improve concentration, attention, patience, etc.