"Mummy, my vulva's itching," said the concerned five-year-old daughter of a colleague in a long queue at a Tesco checkout. There are, it seems, downsides to teaching infants the proper names of body parts.
But for campaigners who prefer limited sex education, mild public embarrassment isn't the main problem. For them, teaching children to call a penis a penis in the same way as you would name a hand or a leg is the first step on the road to perdition.
"All body parts, all on the same level. Then you teach them exactly how sexual intercourse is performed," said one. "By the time they're 11, any natural reserve they might have had has been broken down. It's setting them up for sex, effectively normalising sex for them. It's a significant part of the chain of events that leads to teenagers becoming pregnant and having abortions."
They believe the answer is to teach children that sex before marriage is always wrong, that virginity is a virtue that should not be surrendered, even if one never marries, and that sex outside of marriage is never "safe" because neither party is committed to the other. Until recently, it was a message that was more common in the US, but now campaigners are promoting it to thousands of pupils here (see pages 26-30).
It is hard to credit that there are adults around who seriously believe that unwanted teenage pregnancies start with teaching children the correct words for genitalia. It is even harder to imagine that they could give any class bursting with hormones advice that would sink in. Abstinence as an alternative to safe sex does not have a great track record. And teaching the notion that first sex is always "special" when it can be anxious and usually brief is rather touching but not terribly realistic. It's sex as imagined by Disney, circa 1938.
The idea of compulsory sex education for children infuriates conservatives. The world of the tooth fairy and Father Christmas invaded by talk of dreadful desires and bodily fluids. But hey, that's growing up and teachers have to deal with it. It's a shame some parents can't. Ignorance can undermine innocence far more disastrously than controlled knowledge.
It's not just a question of what to teach but when. "The age of 15 is too high. Long before this, at 7 or 8, boys begin to ask questions," opined TES on the subject of sex education. In 1916.
Sex education should be taught at an early age and it should be about responsibilities as well as mechanics. But it is perfectly possible to deplore unwanted teenage pregnancies, sexual peer pressure and the serial partners some parents inflict on their children without reaching the conclusion that abstinence before marriage is the only alternative.
Teaching sexual responsibility should not entail telling children that there is a single, permissible outcome. More than a third of marriages end in annulment after 15 years, while the incidence of divorce among the over 60s has soared. This suggests that serial monogamy rather than "till death do us part" is the preferred option for a significant minority. Statistically, "shag sequentially after a decent interval" is as valid as "save yourself for that special someone". Neither, however, is a message that teachers should feel obliged to impart.