Are my chicks hens or roos?

I am sorry there are no pictures of them yet to show you as a reference, but I will post pictures of the chicks ASAP. I am trying to figure out if I have hens or roos with my 5 week old chicks. Most of my chicks have very small combs and are starting to pink a tiny bit, and very small pale pink wattles that are barely noticeable. All of my chicks are very sweet and get along very well. Some of my chicks are bigger than the others. Their breeds are: Brown leghorn, black sex link, Rhode Island red, Buff Orpington, Barred rock, and the last one I'm not to sure. The Buff Orpington and the Barred rock are two of my 3 week old chicks. It is very strange because the barred rock is the only one I've had problems with. He/she is fairly aggressive and likes to peck at me whenever I try to pick it up. Do you think this is a trait of a roo, or is it just the breed? Also it does show signs of possibly being a roo, and has a bit of red on the base of the comb, and has slight wattle development. What do you guys think??

Thanks!!

-ftfarmer22