They could be Black Sexlinks. Those are created by crossing a Rhode Island Red rooster with a Barred Rock hen. The male chicks are black with white bars on the feathers, and hatch with a yellow dot on top of their heads; the females are black. Either gender can have some bits of red or brown in the coloring too. If yours are Black Sexlinks, then they are both female.
Or your chicks could be something entirely different, because sometimes stores get their chicks and labels mixed up.
In a month or two, any cockerels should have nice red combs. Somewhere around 3-5 months, they should have their adult feathers, which make it easier to tell breed and double-check gender. Pullets will get red combs shortly before they start laying eggs, so probably 4+ months for that.
