Have you ever met a woman who wished she'd lost her virginity at 13? Do your women friends hang over their coffee cups saying: "I waited until I was 19 years old. How I regret it. When I think of all those spotty youths I refused to let have their way with me behind the youth club, I could weep."

Are there men who wish they had, at 13, 14 or 15 Actually, the answer is probably yes. But would they want their sons to gamble with the possibility of starting out in life with a monthly bill from the Child Support Agency, or a weekly date for the treatment of a sexually transmitted disease, or both? Definitely not. Good parents want the best of all worlds for their children, and they know the best foundation for that is a proper childhood.

So why are intelligent, experienced, responsible adults trying to make it more acceptable for those too young to know better to start their sex lives before they are mature enough to understand what it's all about?

They will say they are trying to do nothing of the sort. That will, however, be the net effect if consensual sex, between 13 to 15-year-olds, is decriminalised, which is what Professor Kathleen Marshall, Scotland's Commissioner for Children, is advocating.

Her argument is easy to comprehend. Why make pubescent experimentation a matter for police investigation and court procedure? It is surely more civilised to have early sexual encounters dealt with quietly, privately, within families. Let them be referred to the Children's Panel as a welfare issue.

In most cases, this is surely what already happens. I am not aware of significant numbers of the early teens being prosecuted, yet we are told they are, increasingly, sexually active as young as 12. As the law stands, choices exist about how to deal with the teenagers involved. I see no pressing argument to remove the criminal option, even if its only purpose is to underline the dangers attached to early sexual intercourse, especially for girls.

Children are reaching puberty ever earlier - some as young as nine. It is a side-effect of improved nutrition. They are also being introduced to the notion of sexuality ever earlier. It's as if there is a concerted campaign to foreshorten childhood. There isn't. The driving force is commercialism. People try to expand markets in order to make ever bigger bucks. Parents are vulnerable to the demands of their children so clever advertisers create a need in children. They demand and parents spend.

They spend on bikini-style swim suits for toddlers and kitten heels for eight-year-olds. The average child of my generation probably owned three frocks: one to wash, one to wear and one for best. Now girls' clothing will occupy an entire floor of a department store and the average 10-year-old will have a wardrobe to rival (if not out-do) her mother's. Last week I heard two 11-year-olds talking about a "sleep-over" they were going to. They were hurrying home to "blow dry their hair, paint their toe-nails, put on their make-up and change".

Will they be ready to experiment with sex in two years? No. But I can see why they will think they are. Do they need to hear that if they do experiment it will be no big deal? That it used to be forbidden under the law but is no longer? Absolutely not. They need to be nurtured to full maturity in a culture of respect - which starts with respect for themselves.

They need to hear that sex is out of the question because their priority is to enjoy the last years of their childhood while getting a great education which will help them realise their talents and ambitions. They need to be told that the dangers of early sex are the same, if not greater, than they used to be. And that they are much too precious, much too valuable, to be put at risk.

Girls need protecting from sexual intercourse long after they reach puberty. For all their chutzpah and seeming sophistication, they are fragile little things. They might run around half naked and plastered with makeup, but anyone who deals with them will tell you that they are at heart mostly romantic creatures. They are just kids filled with idealism and longing for admiration and love.

Romeo-like, romantic, enduring love is not usually the top priority of teenage boys. Their relationship with their burgeoning sexuality resembles that of a first-time dog owner with an untrained springer spaniel. (Each end of the lead thinks it's in charge.) To legalise their sexual access to equally young girls is arguably criminally irresponsible. It can and does lead to pregnancies they are wholly unfit to cope with. They risk the emotional (and, for the girl, physical) pain of a termination - or lifelong parenthood. This at an age when they should be carefree.

It gets worse for girls. Doctors will tell you how the surface of the cervix doesn't fully mature until the late teens. If girls have intercourse before that, sperm can become incorporated in the cells and the effect can be carcinogenic in the long term. They are also at risk of silent, symptom-less chlamydia which can cause them to become infertile.

Professor Marshall and her supporters will argue, no doubt, that all of the above is already happening. She might ask why criminalising the young will help any of this? The answer is that it sends a message. It says to the children that the dangers to their welfare are so great that the law has ruled against the activity. The professor might equally argue that young teenagers drink, smoke, take drugs and go joy-riding. Yet no-one is suggesting we abandon the laws that forbid them.

Between the ages of 13 and 15, young people can't legally hold down a job, vote or join the armed forces. Why, then, would we make it legal for them to embark on sexual activity that is likely to produce a baby with someone who is also too young to care for it? Surely what we want to encourage is the understanding that greater freedom brings with it greater responsibility.

There is no suggestion of relaxing the law that prevents adults over the age of 16 from having sex with young teenagers. But knowing that it was permissible within their own age group would, inevitably, blur the boundary. It is also the sort of approach that paedophiles welcome. The younger a child is recognised as sexually available, the more they think their behaviour is acceptable.

If parents really want to help children through the white water of early sexuality, they need to take more responsibility. It just isn't good enough to be pestered into buying inappropriate clothes and giving too much freedom. They need to fight back against the social pressure, even if it causes rows. If they want to protect their children, the price is taking a firm line. They must refuse their 13-year-old permission to go out looking like jail-bait. They should get together with other parents to resist peer pressure and to offer alternative, fun, leisure activities; take them sailing, climbing, kite-flying, to gigs and concerts. They must do anything to distract them; anything to allow the young to live like youngsters until they have had time to grow up.