Since my daughter knows enough about sex to know where babies come from I told her that every month the lining of a woman's womb (where the baby grows when she's pregnant) gets ready to hold a baby. If a baby isn't made this extra lining isn't needed and so it comes out of the woman's body. This is called a period and it just looks like blood. Women use pads or tampons to catch this so they don't make a mess.
Obviously I answered any questions she had about it.... Its not a very detailed response but it was enough for her at the age she was. If you want to be able to give good answers to your daughters if they ask you I suggest you prepare some age-appropriate answers. I think my daughter was 5 when she asked.
This is pretty much what I told my daughter when she was younger, except I did not tell her about tampons yet and I did not go into detail about cramps yet. She had some further education at school, a video, which she watched with her female paraprofessional. The other fifth grade girls watched it with other fifth grade girls and female teachers, while the fifth grade boys watched a slightly different film with other fifth grade boys and male teachers. I went to school and watched the videos beforehand and the girl's video was all stuff I had already told her, just arranged differently. It also covered using underarm deodorant and bathing daily, as well as how to put sanitary pads in your underwear. I told them I always answer her questions as she asks them, so if she had any questions after seeing the video, they could answer her questions if they were comfortable doing so, or I could answer them after school if they would jot them down for me. They answered a few questions for her. I bought her some pads and showed her again how to put them in her underwear and I put that pair of underwear with the pad in a ziploc bag in the part of her backpack that has a change of clothes for her. I also bought her own deodorant for sensitive skin and put it in her bathroom. Her breasts have not developed enough yet for a bra, so I bought her some undershirts to wear. Now she says, "I feel like such a grown-up!"
I recommend you find a good book about how your body works for your daughters, McJagger. Then you can start reading it with them right away. The one I found was actually called
How Your Body Works, but I bought it when my daughter was two and it may not still be available as a new book. It has two page child-level explanations about all sorts of things, including reproduction, sleep, the different organs of the body, etc. I bought that book when my daughter was two. This was just after she came out of my bathroom completely covered head to toe in sanitary pads like she thought they were stickers. At first, we mostly looked at pictures in the book and I used few words. Then we would read whichever subject in the book interested her. We have covered reproduction, digestion, how babies grow, sleep and the heart many times. Hope this helps.
