I also wonder, Onward and Upward, at what point in their short lives, and why, some children go from a new baby with a body full of cells with XX or XY chromosomes but no thoughts at all as to what either sex or gender is all about, to a child who is convinced that he/she is not the male or female that everyone around them has always said they are.
What is it that they believe is male or female that they deny having or feeling? What do they expect to have or feel as a male or female, which they don't detect in themselves?
If they observe their mother or father but don't identify with them, do they deduce that they are the other sex/gender? And what if there are older siblings, does their sex influence the gender bias of a younger one?
And what if parents decide to raise their children with no gendering at all, to the point of not giving the child any clues even to which sex its chromosomes are - but the parents themselves cannot help being of one sex or other, so when/if the child identifies with the parent it is most in tune with, is it ikely to identify with their sex and gender as well?
There are many complex relationships involved.