Also thinking about the practicalities in a scenario of this kind, how does an honest and age-appropriate conversation about the sperm donor’s role in the child’s history go, if the father is also the person who gives birth?
I think most people would find it very hard to describe the respective role of the (biologically-male) person who gave the sperm and the (not-biologically-male-but-legally-and-socially male) person who gave the egg and carried and grew the baby in their uterus, except in sexed terms, like ‘man’ and ‘woman’, in their biological meaning.
And if you can get through that without lying or confusing the child, what might the person who has given birth, say when the child inevitably asks, ‘OK Dad, but where is my mum?’
The only way I can see to make explanatory sense of that, would be to say to the child that ‘transmen are men’, that is, asserting that humans can change sex in a literal, physical way, or asserting that humans can be ‘born in the wrong body’. Or otherwise requiring that everyone else has to adjust their language and ideas of what a man or a woman is to include people of the opposite sex in those descriptions.
And the above line of belief, doesn’t seem to allow any room for the healthy conversation that lots of women have with their kids, about how shit gender stereotypes are for everyone of either sex and how basically nobody fits those stereotypes perfectly, and so on.