In my experience, the wattles are the best indicator. At week 7 or 8 the wattles will develop quickly. Then it will be very easy to tell whether it's a pullet or cockerel - males will develop big red ones as well as deep red skin around the beak. There is some basis to conditionally sex them based on the "haircut"; males usually have a "choppy" or "edgy" crest while the hens have a rounder and fluffier crest. You should post a close-up of the face in about 3 or 4 weeks, when it should be clearer what you have.