The only way I know to tell is by the feathers and the comb color...And it is way easier to tell if you have a known hen somewhere to compare to. I got 7 babies and pretty early on you could tell the roosters from the hens because the hens had tiny little orange-y pink colored combs and the boys were red right from the start almost. We got the chicks when they were 2 months old, so that helps a little too...seeing them grow a bit, but they are the only ones I have sexed, and really there isn't a lot of difference in their feathering still, but those big red combs give it away. With no hen for comparison I have to guess they are cockerels by the redness of the combs.