It's something I feel very strongly about.

When you can't tell a kid's sex from their genitals, you have a 50/50 chance of guessing right and guessing wrong ruins their life. So why are we guessing!

Most people develop a gender identity between 3 and 5 years old. Unless the child is weakly-gendered, they'll tell you, like I said, before they get to kindergarten. And if they don't and need a bit more time, then let them be non-binary. I don't know how many intersex people do indeed grow to have a non-binary gender identity, but there must be some.