That is NOT a Delaware. See what looks like a pea comb (could be the pic, though) and solid black hackles? Delawares have single combs and barred hackles. It almost looks like a Brahma with no leg feathering, but it is definitely not a Del. You find white legs, single combs, solid black hackles and black tail feathers on Light Sussex. Are the legs white as opposed to yellow and the comb single? If so, I'd say Lt. Sussex.
I don't know if the others are Leghorns or White Rocks. The hatchery white Rocks are pretty slender much of the time so at a young age, it's hard for me to say.