It's pretty straightforward. Fascism needs an enemy to rally it's supporters against. A big part of the "fun" of Fascism is destroying, humiliating, and killing a designated enemy. They need an enemy that is unpopular with the majority of society so their entire base can be turned against that enemy.

The way it goes is the Fascists pick and enemy. Doesn't really matter who it is. Could be Jews. Could be Socialists. Could be trans people. Could be redheads (CW: depictions of racialized violence). It literally does not matter who the enemy is, they just need to pick an enemy.

Then the fascists can blame literally every bad thing in society on that enemy. Doesn't matter if it's true or not, that's not the point. The appeal of Fascism is largely in the thrill of being part of the "In" group and enjoying the adrenaline, cortisol, and oxytocin of ganging up to hurt the "Out" group. It's getting a whole bunch of your buddies together and beating to death someone who is ontologically evil. You get the high of engaging in physical violence, in being righteous, in doing something "Good" to protect your "Volk".

Right now the enemy of choice is trans people. Trans people are a small minority. They're socially, economically, and politically marginalized. No one with any power will stand up to defend them. The majority of society views them as deviants at best.

All of that means the fascists can engage in pretty much whatever violence they want against trans people.

The point is the violence, but they justify the violence to themselves and others by accusing Trans people of all the worst things they can think of. Right now they've decided to accuse trans people of hurting children. It's basically the worst thing you can do, so they're accusing their designated enemy of that. It doesn't matter that it's not happening, they don't care. They're just looking for an excuse to commit violence against someone who can't fight back.

That's ultimately all it is. They want to bully someone who can't defend themselves so they can feel righteousness and excitement and a sense of community with their fellow bullies. They picked trans people because trans people can't really defend themselves. And they accuse trans people of hurting children because they think it will justify their violence to anyone who is watching.

I cannot emphasize enough that they do not give a shit about trans people specifically, or the welfare of children, or anything else. It doesn't matter whether any individual fascist actually believes what they're saying or not. What they want is to humiliate and kill someone who can't fight back. Everything else is just window dressing to justify and excuse that act of violence.