I'm going to go with @Gray Farms on breeds... as for the Cochin's sizes... If they are bantam, then yes. I believe in both sizes they are slow to develop, but they should be keeping pace in size for now if they were all standard sized.
Thank you... they are all the same age (at least I think) but 2 & 3 are much much smaller, and not all that bright. The two Easter Eggers tend to herd them to all stay together.