They may realize they are different, which is fine. But at age 5-6 years old, do you really believe they think they are 'sexually different'?
You're assuming this is about sex.
It's not.
Gender is not sex, and yes, they know they're different, in as much as "I don't like girl/boy" things, which varies depending on the gender. Now sure, some kids grow out of it, some kids just prefer the opposite gender stuff (hell, I loved Transformers and GI Joe as a kid, and the My Little Pony I got? Cavalry mounts for the latter), but for some kids, it's a serious, real issue. And when you get kids that age asking parents "When can I have a baby" unprompted, and they have a penis... well that's telling right there, IMO.
So this accounts for what? Probably less than 0.1% of the population. `Kids just don't need to know some things until they are older.
But they already KNOW these things.
And it doesn't matter if it's less than .1%; which might not be actual percentage; it depends where in the world you are and if someone feels safe to answer that they're GLBTQIA+. I mean, in the US alone GLBTQIA+ is up 7.1% as of 2022. You think in repressive areas like Uganda and others anyone who is part of the group is going to out themselves? Hell no!
The percentage of U.S. adults who identify as lesbian, gay, bisexual or transgender has increased to 7.1%. This is driven by high LGBT self-identification, particularly as bisexual, among Generation Z adults.
news.gallup.com
So, .1%? Yeah, maybe not so much. If you break it down into the different groups specifically, *maybe*... but maybe not.
Like most people who are in a tizzy, you are out assuming that as soon as a 5 or 6 year old mentions that they don't feel like the gender they are, people are pushing for them to lop off body parts, throw them into HRT and so on. That's NOT the case, but no matter how many damn times it's said, you keep believing it.
Which is why issues like PRIDE will keep existing despite y'all hating it.