My post on the group:
It depends on age I guess, but if it's not causing them distress I don't really see much need to talk about it, particularly if that conversation risks leading them to reframe their natural temperament and preferences as somehow different. Pointing it out, even ostensibly to 'celebrate' it, just highlights a point of difference, which is hard for a lot of kids. Obviously if a child comes to you unhappy about it that's a different situation.
Instead I think the important thing is to take them as they are and be quietly supportive, while not making a big show of their non conforming nature. Whenever I've read blog posts and articles about 'trans' children, written by their parents, there is more often than not an element of having tried to stop their child, or tried to redirect them to other more stereotypical sex based interests. Given how I see in my kids how much they double down on things if I try and direct them, I often wonder if that approach forces a child to nail their colours to the wall as it were and therefore lose the ability to just be fun, curious and playful about these things.
By quietly supportive I don't mean hiding anything from anyone, I just mean accepting their gender non conforming ways without huge fanfare. My eldest son was very non conforming through to about age 5 (he's nearly 6) and still is in some ways. He liked the female characters best, loved wearing dresses, constantly put trousers on his head to be long hair, play painted his nails (I don't do this so who knows where he got that from), grew his hair long for a while because he wanted princess hair, always pointed out nice dresses, loves pink and sparkles, unicorns, mermaids etc. So I was quietly supportive by treating his interests like any other (which they are, no one minds a girl liking these things, the fact he is a boy is by the by). So he got the princess dresses he wanted for birthdays and Christmases, I helped him make his 'hair' long, his colouring books were unicorns and fairies etc. But I didn't make a fuss about it any more than I would make a fuss about my other son liking stereotypically boy things like dinosaurs and cars. They just like different things.
He wore a princess dress to school on a non uniform day to largely positive response. I didn't say anything to him beforehand as he felt fine going in and I thought even an attempt at saying I was proud of him for doing it would again, highlight the difference when the way I want him to feel is that there aren't male and female toys or ways of dressing, rather than implying he is brave to do something 'different'. As I said mostly it was positive, pretty much all his friends at school are girls and they loved it. He had some slightly mean/questioning comments though from a couple of kids including 'boys don't wear dresses'. When he told me this I just said 'well, boys don't wear dresses that often so some people think that's unusual. I think clothes are just clothes. It's so much fun to dress up as Elsa" and that was enough to make him feel better.
Personally I think two things - one, that people are too quick these days to leap on gender non conforming behaviour, even just to celebrate it, rather than letting kids just have their interests the way they would if they were 'gender conforming' or as I prefer to say 'if they behaved in a way that matches sex stereotypes' which is yes, not the language we use these days but I think brings more clarity to what we are really talking about here. I think if you make it a Big Thing (negatively or positively) you risk the child either feeling they stand out in a bad way OR that they have to stick with their non conforming interests because that makes them special in the eyes of the world and therefore makes it hard to change direction, the ways kids do, if they want to. I think they lose the freedom to explore and be who they are or who they want to be, which should be as conforming or as not as they want to be. And two, it's much harder for boys. Girls who want to play at being a firefighter and hate dresses and love getting muddy are very celebrated and some people even find it hard to have 'girlie' daughters. Feminine boys? Not so cool for some. There's a lot more trans girls (as in male to female) kids than vice versa because I believe society makes more room (not everyone but generally) for tomboyish girls. The ratio shifts in adolescence which is likely linked to the fact that adolescence is arguably harder for girls with the obvious physical changes etc.
Anyway long long post short, I believe in letting kids be kids, as non conforming as they want to be, without either negative or positive fanfare. Why do we give kids exploring a range of interests a label of conforming or not, anyway?
Last caveat, I am looking at this with younger children I guess, being a parent of younger children. I hope to take a similar approach as my son grows though. He's fine as he is and he doesn't need to define himself as any particular label.