This thread by Thorn is illuminating,:
twitter.com/JesseThorn/status/1377287133921116160?s=19
Excerpts:
When she started kindergarten, my wife was bathing her. An adult friend of ours had just come out as trans, and my wife mentioned that not all girls have vaginas and not all boys have penises.
Why would you tell your small child that?! Why?!
Talking to trans friends, I learned why it's so important to clearly tell kids that private parts don't determine gender. Little kids often don't know what "trans" is, so they just assume... well... that they're broken. Give kids some language and they can tell you who they are.
She socially transitioned in kindergarten. She had girl play clothes already that she wore at home when she felt like it, but my wife took her to Target to pick out some clothes. She chose a pink and purple My Little Pony dress.
We still had to (have to) be on guard all the time. Every new care situation (camp, sports, babysitter, friends' parents) had to get a briefing. We had to check every room for jerks. Because being misgendered, or forced to explain yourself is traumatic for a young kid.
When she enters puberty, she'll start taking a pill that prevents testosterone from changing her body. This treatment is safe and reversible, and is also used for kids with "precocious puberty" (puberty that starts too early).
Trans kids take hormone blockers because while stated gender identities are stable starting from the time kids can express them, a ten or eleven-year-old's brain is still growing by leaps and bounds. So long-term decisions about bodies are postponed a bit.
When our kid is in her teens, she'll decide how she feels about her body. She can do nothing and have a "boy's" puberty. She can take hormones and go through a "girl's" puberty. When she's a young adult, she can (if she choses) have surgical interventions.