To me, it's irrelevant whether or not you have an iron-clad case for your suffering or even discomfort.
There are loads of people who can't put into words why they feel bad in some way or another, but that pain isn't diminished or made un-real because they're fumbling around with words that doesn't quite map onto coherence and meaning.
People like
Contrapoint has done a good job at showing how complex and, in some way, "up in the air" ideas of gender is, and how that complexity continues to mature - rather than dissipate - when you transition, because you carry with you all that you've been before you transitioned, and that will always inform the rest of your life (in the same way all of our experiences continue to inform and mutate the rest of our lives).
It feels sorta odd to ask this "Ben Shapiro-like" questions of "if gender is a social construct, how can children understand gender"/"What is your precise definition of gender?"
Where is the humanity?
Why are you holding transgender people to a standard that is fundamentally inhuman - which is, you have to know your essence, and be able to verbalize it perfectly for it to be valid - when the same level of standard is never applied to cis-people, or even people like me, who identify as male, wants to be male, but happen to be gay?
My inner life - and my identity - is in a constant flux, because I am growing older, and constantly experiencing new things. What I was when I was 20 is as alien to me as to be an other person.
I feel like there is an inhuman - and unfair - expectation for transgender/queer people to "explain themselves", that is fundamentally dishonest, because we never turn that mirror around, and ask the other to explain themselves, fully.
Also, you can break down any individual concern on an individual level (which is how you treat these things anyway). An AMAB (assigned male at birth) person doesn't have to have an "academically-sound" reason for feeling other, nor are their feelings less real because you - as an adult - can (I guess, accurately) decipher that gendered toys like guns and dolls are a social construct, and therefor not inherently gendered.
Ultimately, I think transgender people are having a bit of a moment, and some of their previously extremely insular culture is spilling over into the mainstream. I wasn't alive when the first cross-over between straight and gay discourse happened, but I assume it was also messy, tedious and repetitive.
That said, the issues that are relevant for people who are transgender, are not the same for people who are "not-straight". Each have their own history, and their very particular complexity. This also means that just being "non-straight" - like me - will not prepare you for handling transgender issues.
My long-winded point is that it is weird for supposed allies of LGBTQ+ to fall into the trap of assuming that transgender people have a ready-to-consume explanation for their existence.
I'm 36, and I don't have any coherent explanation for my existence. If anything, I have only more questions the older I get. I'm a failure by most metrics, and yet nobody has ever asked me to do a "facts don't care about your feelings" inventory of my life.
It feels odd to invalidate the very real feelings that children have and express - feelings that I had when I knew I was gay at the age of 9 - by way of trying to hold them to an academically rigorous standard.
Yes, children are very tedious, but if you're a functional adult, you can also catch when a child is being very genuine with you.
... This notion that we - adults, as I think we all are, on this forum - can't read subtext, can't understand what it's like to be a child, can't understand other people through our own suffering, can't give other people the benefit of the doubt, etc, is something that I'm frequently annoyed with, and makes me not want to post.