I think it's important to have the sex talk on your terms and not let schools do it for you. The schools can do the biology part very well but you need to handle the rest and I would argue that the rest is far more important.

I like language that's less technical and more qualitative. It sounds corny but lines like "when 2 grown-ups love each other" tell a lot about the things a child really needs to learn: this is for grown-ups, this is for people in love, etc. A 5 year old won't care about ovaries and spermatozoa but will care about love being a precursor to wanting to have a child and they'll be interested to know that their own strange private parts will have the ability to create life when they are older.

I don't think you should wait for her to learn at school (or anywhere else for that matter), I believe it's our job as parents to educate them in as many topics as we can, this way you can build a trust foundation (which is why I won't tell my son there's a Santa or Tooth fairy, but that's a subject for another question)

Going back to the question, did she express curiosity already? I think you should know when it's time to tell her, and I'd go about it using as much truth as you can (without making it pornographic of course)

I strongly believe we should try not to lie (or white-lie) too much to our children (when I was little I hated finding out elsewhere about stuff, like Santa not existing for example :) )

By "learn this at school" it looks like you're talking about via the formal curriculum. However, I distinctly remember learning about "where babies come from" in first grade from a classmate. I can't offer suggestions about how much you should tell your child or how to introduce the subject. However, if you don't want her to learn from fellow classmates, I'd suggest introducing the subject sooner rather than later.

I think five years old is too late. The basic facts about animal reproduction and how their own bodies work are something I believe they should learn from you at a very young age, casually and repeatedly, and with no shame. Remember that this is something every kid would have known (and seen) it on the farm or in the wild, until just a few decades ago.

My three-year old has known for some time that:

• Males and females are anatomically different -- men/boys have a penis and females/girls have a vagina (in mammals). Also various other secondary sexual characteristics like size, hairiness, musculature, etc. And you can see differences (some the same, some different) between males and females of other animals, too.

• It takes a contribution of cell each from a man and a woman, which combine and grow into a baby inside the mommy's belly for nine months, after which it comes out of the vagina. After the baby is born, it eats mostly milk from the mother's breasts/nipples (males have them, too, but they are non-functional).

• This is the same process in all mammals (which we are), but it's different for other families. Actually, he knows it's not quite the same for ALL mammals, he knows about placental mammals versus marsupials. And he knows that birds and reptiles lay eggs, for example, and that only mammals have milk.

He knows all this just like he knows the about digestion, how some animals are carnivores and others herbivores, etc. It's just the very basics about his own body and the world around him. Maybe it'll help you have a natural conversation if you think about it that way, too.

Incidentally, he does NOT know the gory details of how the male and female cells get together (penis inside vagina, etc.), but that's mostly because he hasn't asked for more detail yet. I'm sure that at some point he'll realize that something interesting must be happening at that step, and he'll get an age-appropriate and matter-of-fact explanation of that, too (along with, when he's old enough for it to matter, the info on the specific changes bodies undergo at puberty, relational issues, precautions to take and/or warnings to wait, etc.).