I have to provide my viewpoint since it is so fresh in my mind.
My oldest, Paul, is 11 1/2. I have contemplated for a long time what to do for his first gun. I had a Beretta 686 20ga with 30 inch barrels. We tried that first and I found for his size the barrels were just too long. His arm strength was not there.
So I chose a Savage/Stevens 220 in 20ga hoping once he got good he could switch back to the Beretta. I chose this particular gun because I don't like hammered single shots. I found them hard to cock and they are dangerous for young kids who don't have the strength to cock them. One slip and the gun goes bang, usually in a direction that is not so great. The 220 cocks on opening and its tougher to open than a normal O/U, but Paul can do it. It has a normal top slide safety.
I found one that someone had tried to checker on for a good deal. I spend the better part of early 2017 sanding off the checkering and finishing the stock. I built my own adjustable butt plate, which in my opinion is key for young kids. I shortened the LOP to ~12 inches. I opened up the full to modified first. I got one forearm panel checkered before we started shooting. The other item I would recommend is getting a Bear Tooth Products neoprene stock cover. Adds about 1/8 of an inch of cloth and foam rubber to the comb of the stock. Makes those first recoils easier for young kids.
I also used the 16ga.com reloads info to find a suitable low pressure 20ga 3/4oz load for Paul. That was another huge help.
I made a pact with Paul. Once school finished he had to shoot with me at least once a week till dove season. He held up his bargain first by shooting trap at the local range here in Denver at the state park. Once I felt he had that down I knew he needed to learn swing so off to the skeet range we went. I tried the modified but I did not feel he was getting the full advantage, so I opened up to IC. He really loves that game better than trap and boy am I glad. I love skeet more than trap too. Along with all of that he made it through a firearms safety course earlier in the year and then did his hunter safety course this summer.
Toward the late end of August I brought out the Miroku 20ga O/U I have had in the closet for almost 20 years and he fell in love.
Although he begged me to let him shoot it for dove season I kept to my original intentions and he shot the single shot. My 9 year old went with us as bird boy for the first time and I really needed Paul to be safe. I chose not to hunt but sat on a bucket in the field right behind Paul and gave him advice, encouraged him and helped him spot birds.
It took most of the morning but he got his first dove on a great crossing shot. He was so excited. I can't wait for pheasant season. I think we will quickly move to the Miroku. By dove season 2018 he will be onto either the Miroku or the Beretta. The Miroku is better for him as he is right handed but left eye dominant and the gun has had the stock modified for a left handed shooter, which his how I made him shoot from the start.
If Skeetx comes along and sees this he might be able to vouch for the gun as he saw it this summer at an event we both visited down at the Whittington center. Paul and I enjoyed a couple rounds of skeet at the Whittington center too.
Just my two cents.