I don't speak for the parents or the little girl I'm going to write about in this post. I want that to be made clear. That being said:
My daughter has a friend who has very clear ideas of her gender identity at the moment. Her parents without getting to much into the details are your typical parents from the west, liberal, but both you could from a distance say fill their generalised gender roles, i.e. the father is more 'masculine: very active in sports and likes his beers; and the mother is more 'feminine' likes to do girly stuff, go shopping and drinks wine.
Taking some broad strokes for sake of simplicity.
My daughter's friend prefers dressing up as a boy. And when my daughter and her friend discuss books from the latest series of books they've shared, her friend will always relate to the male protagonists. The friction between my daughter and her friend often comes down to my daughter wanting to do 'girl' stuff, and her friend wanting to do 'boy' stuff.
The parents have expressed I wouldn't say concerns for their daughter, but concerns on how to be properly supportive of their daughter.
I'm talking about a girl who when all this was happening was
5 years old! She's a little older and still feels much the same way about herself. I haven't used gender pronouns here because she hasn't expressed what gender pronouns she prefers. Her parents and the community (including ourselves) have been mindful and respectful and supportive to whatever this lovely joyful little girl needs.
I think what impresses me is this girl's confidence in knowing a part of who she is already. This isn't a flight of fancy or role playing. My daughter (including her friend) flits from role playing their favorite characters from whatever series of books they're reading at the moment.
"I'm a dragon master and have these powers!!"
Oh yeah, that's cool, what's your dragon's name.....
"No daddy, that's so 5 minutes ago, I love unicorns and my unicorn has twilight moon powers!!!" (I forget which series of books that's from but it is from a book, iirc)
Oh yeah, okay unicorns, cool, cool cool cool.. what...
"Unicorns? What I don't like unicorns, I'm at
Upside-Down Magic school and I'm a 'fluxxer!!!'"
Wait, what's Upside down magic, and did you say "fluXXer"?
And through all these changes and books series and fantasy role playing the one thing remains constant, my daughter's friend still prefers to do 'boy' stuff and relates to the 'boys' and role plays the 'boys' in these stories.
Totally random off-topic minor rant: I thought playdates were to keep kids busy. Yet whenever my daughter's friends come over for playdate, other than the usual snack breaks when I get up and get the tables and snacks sorted, you'd think I could sit back and focus on my stuff.
But nooooo!!! Every 10-15 minutes these kids come out, hover around me while I'm on my computer and wacom tablet, and then ask me what i'm doing. I answer politely and then encourage the kids to go back and play in my daughter's room. Inevitably another kid comes out, or they all come outside and hover around me while i'm either doing CG or illustrator work and end up asking me a million questions. Which I answer politely and then encourage the kids to go play.
This happens enough I stop working and tidy my laptop and wacom tablet away.
I then pick up a guitar I have sitting around the living room - and
strum as quietly as I fucking can - and sure enough a little head pops out the door then a foot and then a shy quiet walk with very curious eyes with questions I can see floating in front of them that I'm soon to hear. Before I know it all the kids are out asking me questions, my daughter shouting above them all "my daddy is a guitar player he has so many guitars even more in other rooms, but you can't touch them, even
I'm not allowed to touch them!!"
Aren't playdates supposed to be for kids to play with each other instead of asking a parent a million questions of what they're doing every few minutes.
While that is off-topic it serves a purpose in that I've had the annoying pleasure to see these kids interact, kids of wildly different personalities, self esteem, confidence, and cultural backgrounds.
So when this little girl who identify's as a boy I can tell you it is sincere and it isn't a fantasy role play. Because some kids you can see they're remarkably self aware of who they are and what they want to be. Wether that all changes in adolescence, early adulthood, late adulthood, that's not a path anyone can predict a future trajectory.
So while it's not necessary kids in general know their gender identity so self assuredly at a young age, that self discovery is bound to happen regardless. We as adults can't be the arbiters of when this happens especially when as adults we become corrupted by a mishmash of social/cultural messages growing up along with vague memories of what it was like being a child at such a young age - which to many grownups idealise as having the better more resilient generation than the next generation ahead of them.
I hope my experience adds to the topic at hand.