Children are curious and they "play doctor" on their own. Teaching young children in a safe setting the difference between boys and girls and what appropriate touching and affection is is important. There is more to sex education that the act.
I think people read or hear "sex" education and think of the act and forget that "sex" is synonymous with "gender." I think children should be taught what makes a boy and what makes a girl and I definitely think they should be taught what is considered appropriate and inappropriate affection (giving and receiving). Teaching children this is one unit of sex ed, leaving the puberty and sexual protection units for closer to junior high/high school.
I agree that children should learn about their bodies BUT I don't think a school teaching 5 yr olds about sex is right. The younger they learn the younger they'll start wondering as experimenting. My son is 8 and knows girls have vaginas, men have penises, how babies are born and about females having periods. I don't think my sons age is yet appropriate to know about intercourse. The younger he knows. The sooner he will want to experiment.
Children should learn about themselves and others at developmentally appropriate ages. I fully believe if this happened we would have far more tolerant and respectful children, far too often kids learn it from TV or movies and the parents are too embarrassed to talk with them so they shove a book or movie about it in front of them. When my son was around 3 when he started saying that girls had penises, so right away I taught him the correct term for what he had and what a girl had. We were in the grocery store one day with a friend she said how smart my son was so I decided to show her what he knew. I asked him what girls had (thinking he'd say boobies,) but clear as day and loud enough to make people turn around he said "girls have vaginas!" I turned a little red.
Developmentally appropriate education about your body, healthy relationships, and healthy boundaries is important to helping children grow up understanding how to be healthy, respectful, respected and safe. When we open the conversation to young people we help them learn body confidence, healthy boundaries & consent, which helps protect our children from becoming victims and/or predators and gives them confidence to report inappropriate behavior.