These guys telling you to get a pump are incorrect IMO. And, those telling you to put a 12 gauge in a twelve year old hands are way off base. You could ruin the kid by hurting their shoulder.

An autoloader is the best bet. My gun dealer sold me a 20 ga. Remington 11-87 adult model then advised me to get a youth stock off of Ebay. That way they have one to grow into. It works great. Have the kid practice with 2 3/4" low brass so as to not get shocked by the recoil. Switch to a turkey load on the day of the hunt. With the extra clothing and all the adrenalin, they will never know the difference. I would recommend that you pattern the gun with the turkey loads to make sure they work.

Keep the shots close. Another bit of advice is to put the kid in between your legs. That way you can coach them right throught the process by whispering in their ear - at least the first time.