We have the 510 my 9 year old likes it was the only one she could hold up and operate. Safety was an issue. For a youth gun it was tight I got blisters trying take it off safety took it to a gunsmith 25 bucks problem solved
I'd recommend the Bantam in .410. They have interchangeable stock extensions that let the gun grow with the kid. The 870 youth was just too long for my son when he was younger. He went from the 20ga Bantam to a Remington 1100 in 12ga and was happy to not get kicked as hard!