On the other hand I am not sure there is an innocent first stage where attraction to kids is a relatively harmless fetish and not a heinous paraphilia?
I can't see that either. I read an article many years ago by a German sexologist - this is purely from memory so I'm probably garbling it - but he was writing about conversion therapy, and also about the Catholic priest scandal and the once fashionable idea that you could cure paedophilia through therapy. His view was that sexual orientation might be relatively fluid in adolescence but by about 18-20 it's fixed - that was his argument against conversion therapy.
From memory, he seemed to be arguing that it makes sense to see paedophilia as a sexual orientation, but unlike homosexuality, there's no harmless way to manifest it, it just has to be suppressed.
I'm not sure, except we can agree that there are certain desires - because they're inherently harmful or relate to those unable to freely consent - that society doesn't tolerate.
Instead I believe that all medical transitioners are mentally unwell by definition, but of those some are so sexually motivated that it reaches mental ill health levels and leads to transition, whereas others are simply mentally unwell without the sexual motivation. That latter group would include gay men who believe that they should really have been born straight women.
I basically agree, and I think we can see that with young female transitioners where there usually isn't a sexual motivation, but there's invariably a mental health element.
I think therapists know there's a strong relationship between paraphilias and poor mental health, and they often feed off each other. I've only known one women who was a fetishist bordering on paraphiliac, and she differed from the archetypal male paraphiliac mostly in being aware that her obsession was unhealthy, and if she wanted real life relationships she would have to bargain down from the scenarios in her mind; many male paraphiliacs wouldn't have that self-awareness. But in this case (no trans element) she had other mental health issues.
The strange thing about cross-sex identity is that so much of our society, even health professionals, have trained themselves not to see either fetishism or mental illness as soon as the magic words are spoken. Though in many cases I think they do see it, but pretend not to.