I am no help on the other breeds, but... I have had blue cochin chickies a few times and what I have noticed is the tails. The girls get tail feathers sooner and the boys look tailless much longer maybe 8 days longer.OK Delsih-you have me stressing now! They sold these as sexed pullets-better not be any males in there!!!
If you are waiting on cochins to Crow or lay eggs, you will be waiting a long time. I had a blue roo that did not crow until he was like 11 months, maybe because of the other roos sounding off around him, but for sure he was full grown.
JJ