All of their feet look the same to me though lol4 weeks is a bit too young to be sure, but you will start noticing differences at this age. I managed to sex my Silkies by about 5 weeks.
At that age, what you're looking for is a larger flat wide comb and large legs/feet, and they would be the cockerels. It helps when you have a few of them because then you can compare. I only had 3 but 2 of them were males, so I actually noticed differences in the hen first, mainly that she was generally smaller than the other 2, had a smaller comb, head and legs/feet.
Mine are only 9 weeks now but here's a couple of pictures of leg comparisons.
This is the hen.
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Here's one of my boys,
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The boys legs always remind me of dinosaur legs for some reason!