Hens or roos? Also what age can I tell?

[Kaleigreenlaw]

Pretty sure I have at least one roo. The comb is turning pink and he/she is 3 weeks old today. Pictures of my 3 in question below. Also my all black chick is acting like a mama hen to the 2 new babies I got, could this be a sign of a hen?

 

[keesmom]

Where did you get them?

 

[Kaleigreenlaw]

Where did you get them?

Local people in NH

 

[NatJ]

Pink-comb is probably male.
I don't know about the black one. (Be aware, black combs don't turn visibly pink at a young age, so they're harder to sex.)