I don't know if any adapt very well. Youth models come with a short barrel to balance with the short stock. Lengthen the stock and it's out of balance. And if you shorten a standard shotgun you're starting them off with a shotgun that's out of balance the other way.
Our local 4-H Shooting Sports for trap shooting has Rem 1100's and 11-87's in 20 youth and they work very well for the kids though they can be a little on the heavy side for the smallest. We like them for the soft gas system and shooting one shell at a time the action locks open for safety. We have an 870 in 28 but you loose the felt recoil reduction and the shells are expensive. A couple of the kids have 870s and do fine.
My favorite is the Franchi 720 20 ga. that Pheasants Forever gave us. It's substantially lighter with an alloy receiver and is gas operated so you still have the reduced felt recoil. If a shooter is having trouble with the weight of the Remingtons we get him on the 720. I can manage a short stock, more or less, and it's just fun to shoot. Points like a dream. If you can find a used one grab it. Can take 3" shells, you turn the piston around to compensate.
When the kids outgrow the 20 youth models they all want a 12 ga. but then it is trap shooting.
