Physical knowledge in textbooks is enough.
Now there is knowledge about physiology in textbooks. Some teachers may not talk about it, but most teachers will briefly talk about it. Even if the teacher doesn't say anything, the students will read these physiological knowledge privately (children in this period are very curious about physiology, so they will focus on learning the knowledge about physiology in textbooks). The physiological knowledge in the textbook was enough for the children at that time.
Moderate sex education
So I think this knowledge is the best for children, and the physiological knowledge in this textbook is enough.
Talk about the harmfulness of sex appropriately.
Although I don't recommend parents to educate their children about sex, I can talk about the harm that sex brings to their age (in this era of Internet explosion, children will gradually understand when they are old). But they often ignore the consequences, so the most important thing is the harm brought by popularization.