I know it wasn't one of the choices, but what's wrong with a single shot 20 for a kid's first scatter gun?
Make the first shot count, probably not gonna be a second.
Not a bad way to go, except most stocks on them are horrible. They recoil all out of proportion to what they are delivering.
At 10 my son built a stock for a 20 gauge Remington 31. A touch of cast and it is very delicate in recoil.
