I have three sons who went with me without a gun a few times before they were allowed to carry a gun, even though they were experienced hunters of other game. Getting a good idea how its done beforehand cuts down on frustration and mistakes when its their time to pull the trigger. Turkey hunting is unique in some ways.

20 ga. guns make good turkey guns, unless you just like to see how far you can kill a turkey. As long as your goal is to bring the birds into good range (within 30 yds), you will kill them just as stone dead with a 20 ga. load of 1oz. #6s as you will with a 2 ozs. of #5s from a 3.5" 12 ga. (One of my sons killed a turkey at 55 yds with a load of 3" #5 Hevishot from a Benelli Nova 20 ga. It was a novice mistake made by an anxious boy, but it just shows that a 20 ga. can be a very effective turkey gun.)

If you don't have too much turkey hunting experience, I'd try to get someone to take you with them a few times to learn as much as you can before trying to take your boy out yourself.

Hal