Leg color should be considered along with the spot on the head and the down color.
Males will have: lighter legs, greyish rather than black down and a poorly defined head spot.
Females will have: dark leg wash, black down and a well-defined head spot.
Most of your chicks don't seem to have head spots - are you sure those are BR and not sex link? Where did you get them? Did you accept substitutions? I'd be suspicious that they're not barred rocks (though black sex link are a BR/RIR cross and will be great layers also).
Males will have: lighter legs, greyish rather than black down and a poorly defined head spot.
Females will have: dark leg wash, black down and a well-defined head spot.
Most of your chicks don't seem to have head spots - are you sure those are BR and not sex link? Where did you get them? Did you accept substitutions? I'd be suspicious that they're not barred rocks (though black sex link are a BR/RIR cross and will be great layers also).