since nobody has given an explanation yet I'll try to, however I am horrible with getting my words out and someone else can give a way better explanation than me.
Most trans people will either have signs or know that they are trans before they are 18. I myself knew that something was off about me as early as 3rd grade, I saw a tomboy and told my parents I wanted to be a 'tomgirl'.
By the time puberty hits is when irreversible changes happen to the body. This is also when most trans people really get the "oh shit this ain't right" moment.
Imagine being trapped in a body that is doing its very best to rip your soul apart from you, then learning that there are medications that can stop it, but then learning that people who aren't even experiencing what you are have made the choice for you to not let you access them.
Now imagine that, for 5+ years.

It's torture.

Don't worry, I support trans kids not being allowed to vote before the age of 18.

"The world is better with you in it and you're worth fighting for!"

You: It isn't and you're not.

Also you: Why is this downvoted??

It's different to voting though.

Puberty blockers have been used for decades with no ill effect. It literally just delays puberty, which is irreversible once a person starts to go through it. It's much safer to delay puberty in children who identify as trans, allow their brains to develop, and have them get treatment so that their mental health is kept healthy.

Personally, I think listening to the trans community on this and having them give advice on how to manage trans kids is better than leaving it to general society who won't understand the emotional trauma involved. There's a reason why suicide rates are high with trans kids.

I would associate it moreso with children trying to tell adults about the priest who keeps touching them but end up being dismissed because they're kids. We ignore our children's voices to our own detriment.

I fail to understand why this gets downvoted ...

Because trans kids exist whether you approve of them or not.

I understand it being a sticky issue for people because there's so much of society and choice we put into the realm of adults. But here's the thing. Psychology has been obsessed with trans people since the origin of the field. We have a ton of data on what happens when trans people recognized at an early age grow up and what that looks like when there's no intervention whatsoever. The reality of it is that there's certain things that there is no medical fix or take backs for once you experience your first puberty.

We know very well that gender identity observed in trans kids is stable. We have a rubric of diagnosis stable enough to have gone up against several National medical ethics boards and survived the scrutiny nessisary to opt for attempting risks.

The first generation of kids to grow up utilizing this process are now adults (the oldest cohort are now in their 30's) and the results have been promising with an almost absurdly low rate of regret reported across the population...

But now you have to recognize why that rate of regret is so low. You need the signoff of a team of professionals who put the bar very high to allow candidates to attempt these risks and any of them can pull support if something doesn't go to plan. Furthermore a child alone does not make these decisions the informed consent has to be demonstrated by the child and their parents. So when people say "kids shouldn't make these decisions" you're missing that they aren't making these decisions. A kid and a panel of adults who are experts in their field, social workers and dedicated parents who have watched the difference in their child's behaviour go from very obviously not thriving in a multitude of ways to massive improvements through social transition make these decisions.

People act like it's as simple as a kid showing up and asking for a lollipop. It isn't. We have literal generations of data about what happens if we do nothing. The outcomes are miserable. We can afford to try something different than known miserable outcomes.

I fail to understand why this gets downvoted …

Because you're a moron who refuses to learn better.

Have you ever felt gender dysphoria?

In a bigoted world, even the existence of the oppressed is a strike against bigotry.

Survive, and the world is better for it.