Help? 4 nee chciks

[Selenyx]

As my family and I were driving home from the movies yesterday, my mom noticed a sign that said "Silkie chicks for sale" of course, since my last chicken (an americuana) was killed by a raccoon, my dad and I have been refortifying the coop so I could get more chickens, so my mom turned the car around, and we bought 4 chicks. The problem is- the owners we got them from didn't know their gender, so of course we don't either.
Any tip on how to determine their gender?

 

[hxgumdrop]

once they are around 4 weeks old or older post pictures on here
https://www.backyardchickens.com/t/579215/silkie-sexing
lots of help on here

 

[hxgumdrop]

They are a real hard breed to sex so it is easiest to tell when they start to lay or cockle doodle doo! roos do tend to get a big comb the ones tht i had looked like brains!
Here is a pic of my roo fully grown then two of my hens. On the last photo the two roos are lookin at the camera and two of the hens are not this is when they was around 4/5 weeks old so you can kind of see the difference but its still pretty tricky!