There is never a time when gender norms are more strictly enforced than during childhood. When you’re an adult, you can present yourself any way you want, and most people won’t question it to your face, but kids pick up on the slightest deviation from any norm. The reason they do that is because the adults in their life are judging people based on their gender expression, but they’re just not doing it around the people they’re questioning. Children will listen, and they will especially listen when they hear their mom saying, «Did you see that woman at the grocery store who didn’t shave her armpits? Please promise me you’ll never do that when you go to college.» 

Sometimes kids scrutinize the interests of others based on whether they seem like a «boy thing» or a «girl thing,» even far beyond typical playground jaunts that you’d think they’d grow out of by high school.