I have White Leghorns and my advice is wait. Because the hens have combs that would put most cockerels to shame. In my experience you can't sex White Leghorn chicks with any confidence by the size or redness of their combs. I've got it wrong before when the difference in comb was a lot more obvious than these. You may get the pullets right, but it's likely some of those you think are cockerels are in fact pullets. I ringed the one with the biggest redest comb (from a hatch of 12) at six weeks to keep for breeding. Turned out to be a pullet!
Thanks, will keep that in mind.
