Probably a Barred Rock pullet.
I have 5 that look like this one. This has the most muted coloring Barred Rock, coloring implies cockerel, but it is too young to be sure.
This is the coloring of the other 4 black ones.
here's a new pic of some of the babies. They are very active now, we have a roost bar 6" off the ground and they flap (or scootch up via the stick ramp) to it easily. Only 1 has a big comb so far, its the black and white. The others are black and grey, brown patterned, and one with a white chest and brown and gold back.
I only have 3 skiddish ones, the others will come right up to the fence when I go check on them