My son is 6 and weighs 50 lbs wet. He can tolerate the recoil of the 20 gauge with 7/8 once target loads. A 3" turkey load is a real thumper. I'm sure it would knock him into next week, and probably ruin his shooting. The high brass 2 3/4 is also too much for him to try.
What I've done is fill the syn stock with lead ingots wrapped in plastic wrap and a rag to fill the rest of the void. Of course this makes the gun a lot heavier to shoulder, so we also put the Caldwell bipod on the forearm as well. I got the longer ones so he can shoot even if he is standing.
Another alternative is to use "Little Skeeter" gauge reducers. Midway has them and for 50 bucks for two and then you can have a 410 shotgun as well. Just plan on getting the turkeys real close. I saw some 3" #4 shot 410 that should take a turkey. Those gauge reducers will also work in a pump, just try not to let them fall on a stone, because they are aluminum and will chip or dent.
Also if you plan on the youth model, it will probably come with a modified choke. H&R sells extended turkey choke tubes, but when I tried to buy one the were out of stock and I settled for a full choke. If you call them they will tell you it is a winchester choke, but it is a specific thread and pitch. Someone told me before it was a invector type , but not the invector plus, so be careful.
I hope this helps. Goodluck and congratulations.