If you post pix we can try to help now if you can't then...
Do any have 5th toes?
Are any crested?
What color are their legs?
Do any have beards?
Do any have feathered legs?
...If so do they have alot of feathers or are they lightly feathered?
What size are they? (any bantams?)
What type of combs do they have?
What eye color do they have?
Do all of them just have white spots on their heads or do some have white markings around their faces?
How old are they right now & Where did you get them?
By 4 days or so you will be able to tell the barred ones from the blacks, mottles ect.
Some "black chick" breeds & what they look like as chicks:
Maran: pink, white or flesh colored legs, single combed, may or may not have light feathering on legs, hazel brown or blue/gray eyes...not always 100% black, they may or may not have some whitish down on their chest, tummies & booty area. Black chicks may be.... Cuckoo, Black & Birchen, vary rare but also could be Mottled as adults.
Barred Rock: blue/gray eyes, yellow feet, single combed, mostly black chick with white spot on their head. may or may not have a little bit of white down mixed in their fluff. can also be Silver Penciled, Silver Laced or Black
Barred Holland: looks very much like the Barred Rocks, in fact you may never be able to tell these 2 breeds apart unless you are a HUGE fan of one of the breeds, a judge at a show points it out or you love, love love genetics!
Australorp: Black chick with white on chest & face, the wings come in with some white feathers that molt out to black, black, blue, gray legs that has some pink mixed in offen looking like multi-colored toes, the beak may also be multi-colored, gray or brown eyes, single combed.
Langshan: Single combed, dark colored feathered feet, that's feathers do not spread down to the 2nd toe. lots of white on the chest, another penguin looking chick. or in some SQ type lines only a small white spot under the chin., longer legs then a Cochin & not as many feather on the legs. Very sweet birds.
Penedesenca: White around the butt & some on the chest & face. Legs are multi-colored as chicks in the darker colors. Rare breed. Single comb.
Shamo: Compacted body, stands more upright. pea comb, white on chest, mostly pink or yellow legs, may have a light gray strip going down it as chicks. Feisty & Flighty chicks that will start to fight early.
Sumatra: Black & White under side & mottled looking face. Pea comb.
Andalusian: maybe black, blue or splashed, kinda looks like a penguin, single comb, longer body, gray or blue legs that may have a little pink in them. feathers may come in looking Blue Laced. combs can grow in fast but not all do.
Dominique: looks very much like a Barred rock but with a rose comb.
Silver Laced Wyandotte: Blackish chick with a swirly looking face.
Silver Sussex: Black chick with some white around the neck & maybe around the beak & on the tips of wings.
I will add more later most likely, My fingers & brain are sleeping...lol, hope this helps just a little.