If you think about it, they only "look like a boy" because social expectation associates boys with short hair. Going back to african children, hair does not denote sex in that culture, it's usually ear piercing that makes a child "look like a girl".
Interestingly, my 7 year old just started a new school, where girls have the uniform option of trousers or skirts. She chose trousers, for various reasons, warmer, can do cartwheels etc.
When she started none of the other girls wore trousers. They had that bizarre thing of wearing shorts under their skirts too.
For the first week, dd half wanted a skirt to be like the other girls. Second week, i offered to take her to the shop if she still wanted a skirt, but she turned round and said all the other girls had started wearing trousers, as they all hated the skirts, especially with shorts/leggings underneath.