Is it repugnant to write books for children and young adults that deal explicitly with sex?

Is it repugnant to write books for teenagers that deal explicitly with sex?  How about for four year olds?

From the NY Times:
Want Teenage Boys to Read? Easy. Give Them Books About Sex.
By DANIEL HANDLER
"I write books for children under the pen name Lemony Snicket, and I’ve noticed that when I go to Lemony Snicket events, the crowds are about evenly split between boys and girls. But I also write young adult books, and if more than one boy shows up at one of my teen book club events, it’s notable, if not a miracle. Something happens once a young man hits puberty.
...
"It is a gross generalization, of course, to say that what young men want to read about is sex — or to imply that the rest of us aren’t as interested — but it’s also offensive to pretend, when we’re ostensibly wondering how to get more young men to read, that they’re not interested in the thing we all know they’re interested in. There’s hardly any real sex in young adult books, and when it happens, it’s largely couched in the utopian dreams or the finger-wagging object lessons of the world we hope for, rather than the messy, risky, delicious and heartbreaking one we live in."
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And from Haaretz:
Israelis debate: Is it okay for a children’s book to say sex is pleasurable?
The latest work by celebrated Israeli children's author Alona Frankel tells preschoolers how their parents do it. Israeli lawmakers are worried

"About two weeks ago the Knesset Committee on the Rights of the Child held a discussion on sex education for preschool children. The reason was the Hebrew-language book by the author and illustrator Alona Frankel: “A Book Full of Love – How Naftali Came Into the World.”
In the book, Frankel describes how people meet, fall in love and have sex – in one case leading to the birth of Naftali, the curly-haired protagonist of her stories whom every Israeli knows from her popular book published 40 years ago and since translated, “Once Upon a Potty.”
But MK Yifat Shasha-Biton (Kulanu), who heads the Committee on the Rights of the Child, said "How Naftali Came Into the World" raised many questions for her, including whether its descriptions were “a little too much for 3- and 4-year-olds.” Shasha-Biton objects mainly to the description of the sex act in the book, which was published two years ago by the Steimatzky publishing house.
As Naftali’s mother puts it in the book, “When people love each other, they want to be very close. We embraced, we caressed, we kissed, and it was sweet and pleasant. We were wrapped around each other and very close, when the penis on the body of Naftali’s father slipped into my vagina. And inside my body it was warm, enjoyable and exciting. A flood of sperm was ejected from him and became attached to a tiny egg that was waiting in the uterus, a special place inside my tummy.”
During the discussion, Frankel was attacked by the committee’s chairwoman, Shasha-Biton, who although she did not deny the importance of sex education for children, worried about the way it was being presented to preschoolers."