trans people are born their gender. There is a huge difference between cis people and trans people before transitioning with the same assigned gender at birth. Before they realize they are trans, they act as their gender, but convinced they are their assigned gender at birth so they try to do things they perceive as respecting that gender.

this is from my own experience and other trans people i have seen, so it probably doesnt apply to every trans person ever, but i dont think its that big of an assumption for a child to make