One of my grandchildren had a report card in kindergarten with the "no" checkbox for the category, "Knows if he/she is a boy/girl" (clumsy wording approximately remembered). There was one other child in that kindergarten with a similar mark, who was a friend of that grandchild. In fact, each of those children knew perfectly well his and her own gender; they just weren't going around broadcasting it to everyone else. The two kids were not the same gender as each other, but each assumed that the other was what they were until a birthday party involving swimsuits.

I don't know how the other kid is these days, more than a decade later, but my grandchild seems normally eccentric.