sup, non binary person here. I don't really understand someone wanting to use 'they' instead of 'you' either, same as I don't really understand all the other pronouns either, but I just roll with these things when someone makes this kind of request because it causes me no pain. Maybe the kid is super annoying, as you seem to have suggested in other replies in the thread, in which case it still doesn't really invalidate their request to be referred to in a particular way.
I am, as ever, fascinated by comments from people suggesting anything other than identifying as a man or woman is delusional. More than two gender identities have been present in various human cultures for as long as both spoken and written records go back . The human brain is an incredibly complicated organ and we barely understand how it works, so it makes less sense to suggest the for some reason gender identity/expression would be the one thing that somehow worked in binary when literally everything else to do with the human brain appears to function on a spectrum.
Even if you are just looking at biology, then that still doesn't work in binary. 1.7% of the worlds population are intersex and chromosomes in people with apparently 'normal' reproductive organs can still do some weird stuff that leads to various differences in the way hormones act and react in a persons body that means none of us can be placed in neat identification boxes.
Socially, it's a complete minefield, but I don't know, I hope that helps explain some stuff or helps with some understanding of the whole mess. The human brain is weird. We're all a different type of mess and maybe we each figure out how to untangle our own mess by the time we die. When it comes to other peoples mess, you just interact with them as positively as you can so long as they're not actually hurting anyone.
I pretty much always forget to check back on threads I interact with on this forum since there don't seem to be notifications on this website (probably a good thing), so I'm sure I'll completely forget to check back on this one as well. I hope you manage to have some more vaguely productive discussion.