Most kids don't need to figure out what gender they are. They know, whether it matches the genitals or not.

I say most because we don't have a lot of clear pathways for non-binary kids and they do need to figure it out. And some trans kids have more difficulty too because gender dysphoria is, from what I have been told, different for each person, sometimes confused with something else...but the kids who know they want to transition at four KNOW their gender. They have nothing to figure out!