The easiest, and arguably best, solution is to let the kids grow awhile. There's no rush to start shotgun. You don't even start 4-H shotgun until middle school.
The thing about sub-gauges and light loads or open chokes is you need to get on target and fire in a hurry. Doing that with heavy gun fatigue or bearing up to recoil of light guns can bring on some weird reactions. If you've ever worked on learning anything requiring high speed and muscle memory you've had problems getting your limbs and digits to do what you want them to exactly when. Putting shotgunnery on a little one is a factor in developing those weird behaviors you see in competitive shotgunning.
I watched a kid yesterday not fire his shotgun twice, in the middle of a round. His forearm twisted real fast both times instead of the trigger finger pulling the trigger. He looked dumbfounded when the gun didn't go off. This is one of the shooters who's well on his way to a perfect score.
I'd focus on something like 5m BB with pre-teens. I know y'all may be more focused on hunting, but competing under pressure will make a shooter in ways the game fields won't.