How can you tell pullet or roo in Japanese Bantam chicks?

[paddock36]

I wasn't sure where to post this. Is there a way to determine pullet or roo in Japanese Bantam chicks just by looking like you can with some other types of chicks like the roos that are born with spots on their heads. I have six that are different colors that I purchased from Ideal as straight run. There are two different ages. Three weeks and one week. They sent replacements when the majority of the first order died suddenly upon arrival. I'm hoping for at least a two pullets and one roo.

 

[jenjscott]

As far as I know there isn't a way to tell them apart untill they get a little older. The first thing to watch for is a bigger redder comb., then the tail feathers tell on them.

 

[paddock36]

About what age should I be watching. My older chicks already have tail feathers. I noticed that one of them grew tail feathers faster than the others and they are a little longer but then the other two grew them. As far at the combs they are all still little.