I bought What's Happening To My Body Book for Girls and What's Happening To My Body Book For Boys, even though they were only for my boys. I gave them the books when the oldest was in 5th grade. I never thought about it again until I occasionally saw them reading the books. We never talked about it.
I liked the books but the few reviews I saw just now in Amazon had some who were down on the books for being too explicit. I sat in on a fifth grade sex education class once and was shocked at all the information but it's probably the right thing, that they find it all out in settings where they aren't getting false information.
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Time flies like an arrow. Fruit flies like a banana.