When they start getting their feathers in between their wings, Delaware cockerels usually have a lot of black/gray there, and pullets do not. I also think it looks like you got one boy, 3 girls. I can't see the area between the wings on the one that looks like a boy, but the other 3 look pretty white in that area. If he has black/gray there plus that red comb, then he is def a boy and the others are very likely girls.