The experience of being a tomboy
It seems that many view Laure's predicament as representing a transgendered child. I can see why they would form this view. It's not the view I have because as a child I was a tomboy and the experience of being a tomboy had nothing to do with wishing in actuality to change my sex. I preferred the company of boys and found most girls of my age prissy. I found it difficult and painful when about 8 or 9 the boys no longer were interested in playing with me and bonded with other boys over games like football. Not being a girly girl meant I felt excluded from their company, which I preferred.
I think there's a reason the film is titled Tomboy and unlike others I didn't perceive Laure's desire to play at being a boy as her desire to become a boy. Even the penis shaping was so she could join them swimming from my POV. Her interests did not conform with being a girl and had they known she was a girl the boys would have excluded her from football as they did Lisa. They would not have scrapped and fought with her.
What the film achieves, intended or not, is to show how hard it is for some personalities to fit with the expectations of what it means to be a boy or girl and the painful division between the two, which is different from wanting to change one's body.
I'm a fountain of bloodshare
In the shape of a girl