There is a huge variety of white chicken breeds, and I can only rule out a few. No feathers on the legs, for instance. But what's their comb type, and can we see a close-up of leg color?
White Rocks? Amber Links? Amber Whites? Rhode Island Whites? Light Sussex? White EEs? (Probably not leghorns or Cali Whites as combs are not making you think that they might be roosters. Also, not CornishX, those are huge by four weeks.)
Single comb, so not EE or Rosecomb Rhode Island White. I don't see any speckling either, so probably not an amber link. They seem a little smaller than the others, so probably not a Plymouth White Rock.
Brownish legs are difficult to define. I believe they're called 'dusky white,' which doesn't come up much and is difficult to define, so searching that online will get you practically nothing. Still, you know that the legs aren't bright yellow, which is a start in identifying them.
I'd have to wait to see what color earlobes they develop before really trying to find out their breed, but there are others far more experienced in identifying breeds. Good luck with whatever they are!