Give them a bit longer to grow. Combs (the actual name of the thing that looks like a Mohawk haircut) do not necessarily define gender. That depends on the breed. My Barred Rock hens have huge combs and wattles, the red fleshy parts that hang from their lower jaw.
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Start looking at the feathers, in particular the hackles (like a collar around the head and neck), the saddle (on the lower back), and the tail. A rooster has pointed feathers while a hens feathers are rounded. A rooster tail will be spikey, a hens will be more fan shaped. The saddle and hackles on a rooster will be longer and spikey, a hen will possibly have a small kind of hackle looking area but will be short and round. Hens don't really have saddles and hackles. Here's my rooster showing hackles, saddle, and tail.
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He is a Lavender Orpington. Just as a comparison here is my Buff Orpington hen.
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Same breed, different gender.
So watch for telltale feathers.
Hope this helps a bit. Remember different breeds might be slightly different shapes but these are general guidelines.