I just bought my kid a new shotgun. Gander Mountain had Remington do a special run for them
It is 1" shorter in LOP than the standard youth model. My kid is 4'10" and almost 17 so she will be lucky to get over 5'. She is muscular and athletic though, being a dancer since before kindergarten.
So far she has agreed to go squirrel, pheasant and grouse hunting. I am sure eventually she will go for rabbits also.
Eventually I am going to be a longer vent rib 870 barrel and have it shortened back to 23"/24" and rethreaded for the chokes. The extra couple inches will help on the swing, but from everything thing I see/read, not much ballistically.
We also have an 870 youth slug barreled gun, left over from my boy, that I will use the extra barrel to turn into a turkey gun as my wife, who does rabbit hunt with me, says she wants to go turkey hunting. So I can get a tight choked barrel and it is already drilled and tapped with a scope mount rail attached.
We had looked at the Mossberg 510's. But from everything I read about them, they are vicious little kickers in 20 gauge. They would have been perfect for kids in 28 though. The 410 chamberings are good recoil wise.
I also reserched the Mossberg Bantam, but really liked the 870 better and since we can switch barrels around, it will work out great.
My wife uses the youth model 1100 20 guage I bought for her.