So just let kids be kids

This is a pretty accurate representation of the ACTUAL treatment trans care advocates want. If a little kid with a dick says "I'm actually a girl", then the treatment is "cool, dress like a girl, change your name if you want, do whatever, you say you're a girl, we're letting you live as one."

There is no medical intervention involved therefore all of this is completely irreversible in case the kid does indeed wake up and say "huh, no, yeah I'm a boy after all".

Medical intervention would only happen at the onset of puberty, via puberty blockers. Again, these cause no permanent effects. Instead they prevent the development of secondary sex characteristics which can be devastating for a trans child. Imagine telling a 12 year old girl "no, you're going to grow a beard now and your voice will drop to a bass register and you're going to shoot up to be 6 feet tall and we're not going to let you do anything at all to stop it". Actively administering testosterone to a cis girl would be considered torture. But passively allowing a trans girl's body to produce gobs of it is always presented as the cautious choice. Puberty can be terribly traumatic for a trans child, especially if they know they're trans and know what they want, know what's about to happen and have to live through those changes.

If a teenager who is on puberty blockers decides at 14 or 15, "yeah no, actually turns out I'm cis after all," then they just stop taking puberty blockers and their development proceeds normally. I'm not sure at what age a trans teenager who has been on puberty blockers actually starts taking hormones to kick off the puberty of their identified gender. But by that point they've typically had years of therapy and life experiences to help them make their decision. And apart from genitals, this allows them to develop almost indistinguishably from other members of their identified gender.

There are many built-in failsafes to prevent these therapies from being mistakenly administered to cis children. Claiming that they are damaging or dangerous overlooks the reality of how this process works. And it ignores the real lifelong suffering that such therapies can help trans adolescents avert.

Not only are there built-in failsafes ... but people are acting as though ideologically driven parents force transition on their children when in reality this is almost never the case. Parents don't want their children to be trans. The process is entirely driven by the child's consistently stated identification and wishes. What's vastly more common is that a trans child will repress his or her identity to please society. Most people don't want trans people to exist. As evidenced by the comments here our society is clearly still deeply transphobic. The reality is that most parents would do anything to keep their trans child in the closet.

For you it may be a matter of "let's not hurry" or "it comes naturally" or "being a teenager" or "experiment and learn new things" - but for trans kids it can be literally a matter of life and death.