Hen or Roo?

[celsita]

Common ol question lol.
Now these babies are only 3 weeks old so I know it would be difficult to identify, BUT i feel like i could already tell the rooster to the hens. Opinions?
These are Black Australorp chicks bought from a breeder on Ebay amd hatched in an incubator by myself.

 

[Ecarroll]

The one on the right in the first picture has a big pink comb, possibly cockerel