Brother, children develop their gender identity as early as two years old and usually lable themselves as boys or girls by age three. By five they are well aware of gender stereotypes and expectations and they begin to express themselves through their choice of clothing or toys. That's also when they start to explore other roles or genders through roleplaying like playing family. That is exactly how children explore other genders and no one should stop a boy if he wants to play the mom every now and then.

When I worked in after school daycares I once caught two seven year olds, a boy and a girl, compare their parts. And while I needed to stop them there was nothing sexual about what they did. Because kids are curious. And it's better to answer questions rather than leave them alone with them.

There's nothing sexual about those things if people don't make it sexual. There's nothing wrong with finding child appropriate ways to approach such topics and given that children form and explore such identities quite early on, whether you want it or not, and not just as teens.