Children can be confused about their sex. In fact, as an ex reception teacher I’d say it’s relatively normal between 2-5 year olds. My son once asked if he was going to grow up to be a man or a woman. This needs factual information in a low key, clear way alongside clarity that gender stereotyping is not related to this. E.g boys grow up to be men, so you’re going to be a wonderful man. What do you think men can do? Ah yes, they can and they also can do X Y Z. The only thing they can’t do, is grow a baby because that is something women do.
My son at 3 could have been labelled as a trans child because he didn’t know about gender stereotypes about colours and sparkles and because he didn’t know boys biologically become men.
He is not confused or upset now, he frequently assertively corrects strangers that he is a boy not a girl (he has long hair by choice).
This business of children ‘know’ is bollocks. They only ‘know’ if their parents react in frankly bonkers ways. Poor parents these days are being taught or even required to not correct their children and teach facts. Madness.