If YABU OP, then so am I. Im pregnant with DD2 so my 3yo knows the basics, as in differences between boys and girls, how babies are made, how they come out. She knows accurate terms for body parts, but has chosen to say 'willy' instead of penis (don't know why, she uses 'vulva' for her own bits).
She has a book called 'Amazing You' which covers the basics in an age appropriate way for pre schoolers, as well as a bit about bodily autonomy, safeguarding and consent.
She hasn't asked how the sperm gets into the vagina yet, but she knows where it comes from. If she asks we will tell her, because if she's asking then she is the right age to know (in an age appropriate way of course!).. Surely it's so much easier at this age when they are just factual about it all and not embarrassed?
My mum explained periods when I was about 9, in case they started when I went away on a school residential trip. And I found out about sex in Yr 5 by listening to some Yr6 girls in my dorm on that school trip talking about the sex Ed lessons they had had the previous week. I don't think my mother ever spoke to me about it, is far rather DD had some proper facts from me, that it's explained with context and when she's the right age a proper discussion about consent and her right to say no, than she learns from the playground and ends up with who knows what kind of ideas about stuff.