An innate sense of self.
This is clearly something that you feel strongly about in yourself, and how you feel about yourself is your business and nobody else's. And what you do to your own body as an adult is also entirely up to you. But surely you can appreciate that an 'innate sense' which cannot be objectively observed doesn't give a reliable diagnosis which should result in medicating children's physically healthy bodies.
children who hve been expressing their gender identity strongly
What does this mean? I've already quoted the part of the judgment which indicated that the child in this case liked to play with "girls' toys" (whatever that might mean) and was unhappy when trying to conform to "male stereotypes". There must have been something else going on with this child as well, because surely nobody would consider putting a child on a lifelong medical pathway because they didn't like gender stereotypes. Why shouldn't a boy prefer "girls' toys"? Why should he be forced to conform to male stereotypes?
What else is going on with these children that means they need to have their bodies irreversibly changed, making them sterile and probably lacking in sexual function? How are these diagnoses made? Why talk about stereotypes all the time, when stereotypes are irrelevant to a transgender identity?
In children, what is this 'gender identity' based on? It must be based on stereotypes, because that is all they really understand about the difference between boys and girls. So it seems children are being medicated because of stereotypes.
There are legitimate questions to be asked about the rigour of counselling and option-exploring before following such routes, the growth in the number of FtM transitioners and the crossover with autism. But none of that justifies a 'we know best and you must be wrong' attitude to young trans people and their parents.
But you still haven't explained how an 'innate sense of self' in the form of a 'gender identity' can be diagnosed in a child. Nor why this results in their body requiring such extreme modification to be carried out before they reach adulthood.