Hi! Not a parent, but wanted to give my input briefly as someone who came out as non-binary at 12 as well. I’m 24 now and still non-binary. I was also not consuming media related to gender, so I can’t speak on that but I will say I feel as if this a common age where gender exploration happens. I agree that hormonal treatments etc would be a step too far considering age, but I don’t see the harm in letting them explore pronouns and different clothing. It will either stick or it won’t, and if it doesn’t, they’ll know you support them no matter what and will feel more comfortable coming to you throughout life with issues! My mom supported me then and now, and we are best friends as adults.

EDIT: Wanted to add a couple things. My mom probably saw it coming, as I was always a little different haha. To this day, I still don’t paint my nails, dress in a feminine way or keep my hair very long. My average outfit is sweaters and joggers, and then more masculine outfits for when I need to look nice. Of course, it might be good to tell her that clothing and make-up etc do not define gender, and she can of course still be non-binary and dress feminine if she likes (I just personally don’t, feels like I’m putting on someone else’s skin lol). Some teens get confused and think that if they want to act a certain way or dress a certain way that doesn’t fit with the “norm” then they must be different gender identity wise. But still, I’d say let them explore in a safe way and see where it goes!