"But I was just pretending to be a boy!"

I can almost hear a future conversation in my head now. It will be between a mother and her "son" - a child who has undergone "gender transition" at an early age.
It's been under discussion in the media lately and it worries me.
I am not a "girly" sort of girl. I never have been. I never wanted pink frilly dresses. "Pretty" things did not interest me.
Middle Cat was even worse. She wore boy's clothes - handed down from her big brother. The Youngest Cat wore jodhpurs whenever she could.
I don't think I ever wished I was boy but I know Middle Cat did. She was the lone girl on the football team. She played with the boys. 
We didn't play with dolls except to put them into what were considered male roles. (Mine was often the train driver.) 
But we were girls. We weren't boys. 
I wonder now though what would have happened to Middle Cat in particular. Would someone have said of her at the preschool stage, "Oh, she should have been a boy. We better get her some transition therapy and start the process."?
Do three and four year old children even really know the difference? Of course they do on one level but I doubt very much they understand at the complex emotional level which says, "I'm a girl in a boy's body" or "I'm a boy in a girl's body". 
I actually know someone who has undergone a sexual transition. It wasn't easy for her at all. It was incredibly difficult and I know that there are still issues for her. We've talked about it.
How soon did she know? According to her it wasn't as a preschooler. 
"I knew something was different about me in primary school," she once told me, "But I don't think I would have been ready to do anything then."
Perhaps it would have been different if she had undergone some sort of gender transition therapy then. I don't know - and neither does she. It's an immensely complex issue. 
I don't doubt at all that there are a few, a very few, people who do need to go through all the pain and trauma of a sexual transition. It must be a  very, very difficult thing to acknowledge and go through. But I also wonder whether the sudden spike in very young children presenting for gender transition therapy is about what they really are or whether some of them are simply like Middle Cat and "a bit of a tomboy" or their parents wanted a child of that sex.
Perhaps we should leave gender transition therapy until a bit later?