They look an awful lot like my hens when they were young. I honestly wasn't clear until they started laying. But for sure if they start practicing their crow shortly you'll know for sure
Brown leghorns have very specific color patterns depending on gender, so differentiating is actually quite easy, these birds are developing male coloring and, at 10 weeks, have the comb/wattle development and coloration of male leghorns, not female.
Agree emma has all cockerels. At this age hens vs cockerels is easy peasy in this color---males have black on the breast, hens have a salmon/brown/goldish color.
Look at the neck hackle feathers. Males generally have pointed neck hackle feathers, females have rounded feathers there. Notable exception is the Seabright Bantams ( both gold and silver ) where both sexes have round feather neck hackles.
Now I am a little concerned... Please see the photos of my four week old Brown Leghorns (I have ISA Browns too). These are supposed to be ladies but now I am not sure. I cannot find a clear image of a female chicks face. Can anyone help?