We got 4 baby chicks from a farmer friend. I think at least two are boys. They are 4 days old today. I think the barred rock is male by looking at his wings.
Feather sexing only works when a variety is bred for that, like Amberlinks. The best way to sex the vast majority of chickens is to watch the combs and wattles for growth and development. If you have several chicks, it is usually easy to tell by comparison. 6 weeks is a good place to start with most breeds, and if you need help, post photos here at that time.