A young boy moves to a new town with his family. He's a goofball, a caring older sibling, and a shy kid. On his first day on the block, he runs into a girl and introduces himself as Mikael. She introduces herself as Lisa, and invites him to play a game of tag with her friends. Later, as he's taking a bath with his younger sister, his mother calls him Laure. She laughs and tells them: "Girls, get out of the bath!" It's almost 20 minutes into the movie before Celine Sciamma upends the expectations of her audience. In Tomboy, Sciamma examines how identity is constructed through performance in childhood, specifically in regards to gender.
The main character of Sciamma's 2011 film is still in that period before hormones kick in when all kids are basically agender in appearance. What separates genders from each other is how they move and how they present themselves.