I have some chicks that are about 4-5 weeks or so old, and I'll be darned if I can tell if they are boys or girls. With the SLW the combs on the boys become a brilliant red far before the girls combs look like anything, and with the silkies, well, I don't even try unless it's an obvious boy (which some are- the combs just pop right up like bow-dried puff paint and others start crowing young,.. and then some boys are late bloomers).
That said, these little fellows have me flummoxed. Nobody has a red comb yet, nobody looks like they are developing wattles, yet there are about 20 of them and I am certain not all are girls. Perhaps if I pull them out of the brooder the boys will have thicker legs, but there isn't an obvious difference when looking in the brooder.