I think you are right....when my black-shouldered babies were that size it was easy to tell, the males were bigger and started getting the darker feathering around the neck.
Its difficult to tell with the angle of the photo. One looks darker than the other. the upper back on the two also look different, but that could also be due to the photo angle.
i can tell you that the one on the left looks similar to my black shouldered cameo hens i have. not sure about the one on the right if it is female or male yet.