The idea of 'trans kids' is important to TRAs in order to win over the public. I used to post a link to a video on youtube when this was mentioned on here where it was explained quite clearly, but it's been taken down now, perhaps because they realised that pointing out their strategy was actually damaging to their cause.
Miranda Yardley transcribed some of this before it was taken down.
mirandayardley.com/en/this-is-an-all-out-political-war-the-gender-recognition-act-and-beyond/
To understand why the focus has moved onto children, look to the YouTube discussion between TransYouth Family Allies executive director Kim Pearson and transgender activist Autumn Sandeen, who states:
“I’ve always said there are two groups that are going to make change in transgender legislation and the “gender identity and expression” related language in legislation. It’s going to be trans youth because … they demystify it and take the sex right out of the trans experience.”
Pearson responds with:
“Right. And it’s hard to say no to kids, and the needs of kids and “keeping kids safe”. And you know, “being respected in schools” and things like that. It’s really hard for people to say no to that.”
TRAs need a constant stream of children identifying as trans, so that they can point to these children and say they were just like that as children, and that no trans people are motivated by a sexual fetish (because that is obviously not what motivates the children). People are also unlikely to criticise children, and instead feel sympathetic towards them and concern about their confusion. For this strategy to work, these children need to be medicated whilst they are still children, because otherwise the vast majority of them will naturally desist once they have been through puberty. These TRAs don't care about children - they are simply human shields and collateral damage.
Giving children mental health support and time to naturally grow out of their gender confusion is also dangerous for late transitioning males, because the focus will then turn to their true motivations for transition.
TL;DR: If you want to legitimise your fetish, make sure it is seen as the same thing as gender dysphoria in children, because that isn't about sex.