My son is shooting a Beretta 3901 Target RL, it's a 12 ga and shoots softer than anything else I've tried, even 20 ga guns. It's not cheap, but it is outstanding! It is available with either a 26" or 28" screw choke barrel, the stock has an adjustable comb, and comes with a couple of spacers which allow it to grow with him. Add a T&S shell catcher and a Briley bolt closer and you are shooting in style! I really can't say enough good things about it!
Prior to buying the Beretta I bought one of the Rossi Youth 20's, it's anything but gentle and does not have a screw choke barrel. If you want to beat the kid up a bit, I'll sell it to you. My son also tried a Browning BPS 20 GA, it worked out well enough but it kicks more than the Beretta and was a pump gun which put him at a disadvantage shooting skeet doubles.
With a nice semi like the Beretta, there is really no reason not to buy a 12GA.
If you are on the South Shore, I would be happy to let you try out the Beretta anytime.