I would lean towars the 28 too . Better patterns , more shot in the pattern . You can get 3/4 or 1 oz loads . I use a 28 quite often wile training dogs and like it a lot . The 410 is more of an "expert" gun with it's small patterns and shot charges . It's just harder to connect with a 410 .
Another option if funds allow would be to look for a gas operated semi auto 20 ga . You can still teach a youngster one shot at a time (just put one shell in the gun)and the recoil will be less . My daughter is shooting a Charles Daly youth model 20 ga and she shoots it real well . There are plenty of loads for the 20 ga too .
So to answer your question . Of the choices you listed , I would pick the 28 . If I was going to buy a gun for a youngster , I'd probably try to get a semi auto 20 ga for the versitility . That Charles Daly was pretty reasonable too , I think around $275 .
Good luck with your decision .