At 8 I would put him in a gas operated semi-auto. True they are a bit more expensive, but you get your moneys worth. Most single shots KICK. A lot of pumps have the pump too far forward for short arms to reach it, and they are either very heavy or they KICK. Recoil is a big consideration for kids.

I shot (and killed) my first deer when I was 6 1/2 years old (thats young... and I was LITTLE). I remember sitting between my Daddy's knees, holding my 20ga SxS Ithaca bird gun stoked with 3" #2 buckshot and that big doe with hounds hot on her heels running out of the only opening in the cutover and locking eyes with me at about 15 steps. Without really aiming I snicked the safety and shot her right in the head, an unbelievable testiment to my marksmenship... or perhaps it was plain old dumb luck . I was as shook up as I've ever been, and I still remember how bad that gun kicked me. I was subsequently afraid of it, and didn't want to shoot it anymore. Wouldn't shoot anything but the Chipmunk (.22) until the next fall. Didn't want to have anything to do with a shotgun.

Dad cracked and bought me a remington LT-1100. That gun has recoil so slight that you could shoot it with one hand, even with a magnum shell. Dad limited me to ONE shell in the gun at a time until I could prove my worth for a season. I shot two more deer that year, and some small game. The next fall I was dove hunting, and then Dad cut me loose with three shells. Started with the 12 gauge when I was 11. Never had the slightest bit of a flinch or gun-shyness since. I still bird hunt with the Ithaca... and it still kicks.

Seriously... a gas auto 20 is the way to go.