I've hatched a few cochin bantams (called Pekins where I live) recently and the braver ones were always boys. The girls tended to stick close to their Mum (I hatched under broodies). Feather development doesn't mean a thing unless that particular strain has been bred that way. By 3 weeks old you may be able to see slightly larger combs on the boys and at 5 weeks old the boys will be growing red wattles and have reddish combs. They are gorgeous things. Looks like you have a frizzle there too (they are super cute).