Good First Gun for Youngster?

My little noodle-noggin is almost 4 years old, so naturally I'm planning his first gun. I figure, considering his level of maturity and interest, that 5 years old might be a good age to get going. The Violence Policy Center, long regarded as a frantic anti-gun organization, has provided this handy website listing several major manufacturers of fine firearms for youngsters. Thanks!

Anyway, I like both the Henry mini-bolt and the little chipmunk .22's. I'm not familiar with the other models listed, and I'm curious about size, weight, safety, and anything else I might have overlooked with respect to guns for munchkins. Any and all advice will be appreciated. I definitely plan to go strictly with iron-sights until he's mastered them, before considering optics. I also want a durable rifle, so it will be around for his little sister to use when she's old enough.

Update: Yesssss! VPC posts this pick on their website along with quotes from some gun experts on how to tell when you're son or daughter is old enough to shoot.