
Definitely not cooperative. I assume it's the one behind the black chick?
Yes, I can see why you think it might be a Cochin or Marans.
From your previous description, I had thought you were talking about a chick with a crest, but I don't see a crest on that chick.
For varieties that could be yellow as chicks, I see that Cackle has pages for French Wheaten Marans, White Marans, White Cochins and Buff Cochins (with the Cochins coming in both bantam and standard size.) Most of those should be easy to tell apart as they grow feathers of different colors.
The black one does look black (yes, statement of the obvious), has clean feet (not feathered), and I'm pretty sure I see a single comb.
So it could be any black breed with a single comb and clean feet. Or it could even be a "blue" breed, because when they breed blues they get some black chicks too.
Poking around Cackle's website, I found:
Black Jersey Giant
Black Australorp
Black Standard Old English
Black Minorca
Ayam Cemani (although I don't think it's black enough for that)
Black Sexlink
I was expecting to find Blue Andalusians as well, but apparently they don't carry them.
And of course I might have missed something, too.