But aren't those little children too young to learn these sordid facts? some parents cry in horror. Well, how sordid are these facts? As one American woman told me, "Honey, boys got bits that hang out, girls got bits that tuck in, put both bits together and you got fun". Of course, many solid and respectable folk share the view of one middle-aged writer - they "don't think sex should be fun". Fun or not, you have only to look at five to 10 per cent of today's Year 6 girls and not a few Year 6 boys to see that these children, incredibly immature though their behaviour may seem, are sexually mature, capable of reproduction - could be parents themselves. For them alone, isn't it irresponsible not to share basic physiological information?
Psychotherapists would call the period between the end of infancy and adolescence the "latency period" when supposedly sexual awareness is low, children bond with same-sex groups, and libido or life force is directed into peer-group activities. This is the perfect time to give information about a topic which will become so heavily charged with emotion later: how much better to know that you can get pregnant if you do it standing up long before someone with ulterior motives tells you that you can't.
For teachers who have not been specially trained - and funding for such training has not been widely available - sex education, particularly in the multi-ethnic inner city, can be a minefield. Might any of the girls have already suffered or be about to suffer female circumcision? It's against the law in this country but none the less there are many young girls who have had the operation and may find description of genitals confusing. Yet knowledge of this possibility may not be appropriate to children from non-circumcising cultures. If there are any Jehovah's Witnesses they may know women who have died in childbirth. And then there are the sensitivities of children who may have been sexually abused.
Yet, with all this, I believe the issues are simple: knowledge is power and power over your body is the most basic form of power. Who are we, really, to deny other people, of whatever age, this power?
Other anxieties centre on whether reading the manual makes you want to drive the car, though whatever else the research shows, it is that sex education certainly does not increase teenage pregnancy rates and may actually decrease them. And surely that is what all we adults, whether on the left or the right, want.
Let us accept for the moment that most parents are benevolent, and that they are the ideal people to give instruction in sexual matters as and when questions arise in the setting of a safe family. Even for these - and I would include my own children here - there is no harm in confronting the shared inaccuracies of the playground with the shared accuracy of the classroom.
At my sons' school there is an excellent three-session sex education programme for Year 6 children. The sessions are taken by class teachers whom the children know well and there is an atmosphere of mutual respect. There is no giggling. The programme begins with sexual maturation, for which boys and girls share the same video but are able to have discussions separately. The second session shows a baby being born and suckled. And the third shows sexual intercourse, with key bits in cartoon form.
Of course, as with all education, teachers cannot control all the learning. My son took in a satisfyingly politically correct attitude that "women have to do so much, Mum, and it can hurt," was emotionally touched by the birth of the baby - "it looked so beautiful at the woman's breast, Mum" - and filled with speculation as to how much hair he would one day have on his body. But his biggest wonder was reserved for the "poor woman. Do you know, for two days after sexual intercourse, TWO DAYS," he informed me, eyes wide, "she has sperm inside her," (doomy pause) "WRIGGLING!" I ventured to suggest that it wasn't so bad as all that, human sperm not being exactly the size of frog spawn. He was unconvinced. "And then," he insisted, "they get Absorbed. Yuk."
Well, that's one person whom reading the manual hasn't made want to drive the car.