I recently purchased a starter shotgun for my boys. A cheap Rock Island single shot 20 gauge that my oldest will receive at Christmas. My oldest boy is a monster at 8 years old, 4'9 and near 100lbs. If he pays attention and does what I want to see him do with this break open gun I'll take him shopping for a bigger pump or semi auto in the next year or so and my younger boys will learn on the cheap break open gun. I really like the idea of starting kids with a single shot, even my mag fed guns as a kid were used one shot at a time with the ammo doled out by my dad when it was time. That being said, the wife just picked up an 870 compact 20 gauge and we're all very pleased with it so far.
I agree with you except for one thing... those single shots are light and they are not going to fit very many kids well due to excess drop at comb. That makes them kick hard for young shooters. I started my son on a 28ga single shot and it was brutal to shoot. I was afraid I had broken him of shooting after the first time he shot it.
