I agree that it is never too early to discuss things. This may raise some eyebrows, but my 5 y/o already knows about periods. She has known since she was 3. She follows me to the restroom and asked questions. At first I didn't address it, but I realized I didn't want her to view her period as shameful, bad, a curse, etc. She is happy with very basic answers. I talk about it like I do voiding or other body functions. The details and objectives of our discussions will evolve as she gets older. Of course, she doesn't know the details of ovulation, etc. I encourage all parents to talk to their kids. It can be uncomfortable for some, but children NEED a reliable source of information. The very young girls I have seen in the clinic do not have the information they need, and what info they have often comes from peers. Many of them state they can't talk to their parents. I am sure you can imagine the information they gain from their peers.
Good luck with the talk.
Autumn
Good luck with the talk.
Autumn