The Ithaca only comes in 3".
You can swing a 10 on a mallard, and other larger puddlers, but divers and teal will show you a thing or two with a 10 lb beast in your hands.
Unless your son is used to the recoil of a 10, I wouldn't do it. I am around 6' 3", 185# and my BPS 10 kicks like a mofo. Not bruises or anything but I can definately feel it when I pull the trigger. An auto would be lighter on recoil. I don't know what kind of gun you have?? Auto, Pump, One of those old Bolt actions???
The 12 will be alot more enjoyable for anything, you are limiting him to geese or pay the price on ammo with the 10. You can't hunt pheasants or upland with it, and the cheapest box of shells you will find is going to be 14.99.
Get a 12, it's a smarter choice. If he wants a 10 have him save up and pick one up on the side, the 10 is a specialty tool. It's kinda like a mini-van and a corvette . One is for everyday use, one is for times when you really need the "goose" behind ya.
