....you are an adult so you know what you are getting into, but if you hatch eggs from kiddies I will fight it with fire. No kid deserves the many diseases that a non developed puberty will bring.
True Story:
Baby Sister (~2) and Little Boy/Big Brother (5) (seriously they respond to those names) were playing and I explained to him that they won't be little forever and Baby sister will grow up and become a woman someday, just like Mommy.
Him: a woman?
Me: yes, and maybe Baby Sister will become a Mommy too, when she grows up.
Him: I am bigger then Babysister. Baby Sister gets big, too.
Me: well yes, Men are bigger then women. Do you want Baby Sister to be a Mommy someday?
Him: I be a Mommy too.
Me: no, you can't be a Mommy because you are a boy and you will turn into a man, like Daddy.
Him: Baby Sister can't talk yet.
.... this is the level of understanding we are talking about here.
Here is another fruitful exchange, between him, and his 7 year old cousin:
Him: if you throw your arm in the fire it gets hot.
Cousin: yeah it burns.
Me: You throw anything in the fire it burns to ash.
Him and cousin: ash?
Me: see, those are ashes. Fire turns stuff into ashes.
Him: can I put my sock in the fire?
Me: only if you want to turn it into ash.
Cousin and him: when can we go to the gift shop?
Him: ... further incoherent ramblings about fire. Cousin listens intently.
This is where kids this age are at. Both are functioning at grade level, etc.
Some kids are a bit different, I admit it. There is always one little boy who chooses to play house or dressups with girls, rather than play with hot wheels. And there is always a girl who from day 1, resented being dressed in skirts and getting dolls for Christmas.
However, don't over think it. And when we impose a master-narrative about gender, and infuse everything with more meaning than children are ready to grasp, we irrevocably complicate the picture for them. Let the kids navigate this world on their own. That is the purpose of childhood really, it is a time to practice for adulthood.