As the mom of an 11yo who pulled an uno reverse moment when I came out to them, I think even just being willing to be supportive is more than a lot of kids will get. I came out to mine as trans 2 years ago and they were like "oh, um. I've been thinking about how to tell you I think I'm nonbinary." They were worried we'd think they were just wanting attention, poor thing.

My suggestion: ask what terms they feel the most at home with, don't just assume anything stays the same unless they explicitly say they want it to. For example: "How would you like us to refer to you? "Child"? "Kiddo"? "Son/daughter" still apply?"

And then ask things like (if afab) "Do you want to be 'one of the girls' or 'one of the boys' if gender split stuff comes up at a party or hangout?" And "If I'm calling for you and your friends - what should I be calling out? "Boys"? "Girls"? "Kids"?

Note: we ask these things not because we want to force them into one, but because we want to help them feel comfortable knowing the answers in low-pressure situations so that they are never put on the spot about it.

Ask about wardrobe, hairstyles, other details of presentation, and importantly: let them try out and enjoy stuff. Or hate stuff. Ours got a should length side-shave haircut and they love it, but you've got to be willing to let them experiment or they'll never get a chance to figure themselves out.