A COUPLE of months ago I was buying shoes for my five-year-old daughter in Tooting High Street, south London. As she agonised over the ones with or without the pretty flowers, I realised my three-year-old son, Billy, was nowhere to be seen.

'Have you seen a little boy, so high, wearing a red and yellow anorak?' I asked the shop assistant. 'Eh?'

I rushed round the shop, looking between the racks of shoes. No Billy. The third woman I asked, clearly a billion neurons short of a full load, thought she'd seen him out the back.

I barged into the storeroom, roaring 'Billy]'. No sign of him.

'Oh, he went out the front with some other children,' said a motherly shopper.

By extraordinarily good luck a neighbour happened to be passing as I stood outside calling for Billy. She offered to look after my little girl (now in tears).

I will never forget the next few minutes. Like a dog casting about for a trail, I ran up and down stopping passers-by and people at a bus stop, until a couple of women said they'd seen him heading that way.

'But he wasn't upset,' said one kindly.

Heart pounding, I sprinted down the road, yelling 'Billy]' at the top of my lungs.

Tooting High Street is quite a friendly shopping street; word spread, and several shoppers called out new fixes on the escaper. Finally I saw a woman coming towards me with him grasped in her arms.

This saintly woman had seen a lone three-year-old trundling over one of the four busy side-streets he'd crossed, head down, legs pumping. She'd stopped her car, grabbed him and brought him back to me.

I didn't collapse and I didn't beat Billy to within an inch of his life. I managed to thank the wonderful woman, grabbed my son and, still shaking, rushed back to where his sister was being comforted.

It makes me shiver even now to think how lucky I was. I doubt there is a mother, father or childminder who has not had the appalling experience of losing track of their charge: Billy had made a getaway once before in Woolworth's, where an old lady tipped me off that he was limbering up for Arsenal in the corner with the footballs. I found him dribbling his (stolen) ball past the gardening tools. I thought that telling off had calmed his lust for adventure; but I was wrong. Thank God I wasn't fatally wrong.

My heart goes out to the Liverpool woman whose toddler was taken and killed the other day. If I could talk to her, I would say don't blame yourself (though I bet she will). What parents are routinely asked to do is simply impossible for a normal imperfect human being.

Children between the ages of two and four can be quite large and strong, extremely mobile, bursting with enthusiasm and curiosity. You can't reason with them until they can talk, and not very much even then. Young primates are designed by evolution to be sociable and adventurous. I've tried explaining to my son about not being friends with everyone (particularly men), but he just yells, 'No, no, no'. He can't imagine a bad person. Everyone he knows, with the possible exception of his killjoy old mum, is friendly, exciting and loves him.

Listen any Saturday to the Tannoy announcements in any supermarket and you'll hear of two or three children an hour who have gone missing in the thrilling confusing wonderland of a modern shop.

Reins stop being practical when the child takes against them, slams all 45lbs of himself down on the lino and howls. A wristlink is made of Velcro and can be undone easily in seconds. Strapping them in a pushchair works only as long as you can keep the pushchair in constant view and until they learn to undo or wriggle from the straps.

The disapproving consensus seems to be that mums whose children escape have only themselves to blame. They should, goes the unspoken condemnation, be vigilant at all times, hold their children's hands, never relax for a minute.

But 100 per cent vigilance is simply impossible to maintain when you're simultaneously trying to calculate how much you can afford, find an assistant, remember your bags, fend off the chit-chat from your other child, prevent juvenile shoplifting . . . . Sometimes your attention is simply split too many ways.

We have never lived in such a mercilessly hostile environment for children. Today's world is designed solely for a young, fit person with no children. We have to guard children against drivers who can't be bothered to slow down, dogs owners who can't be bothered to train their pets not to bite, and evil predators disguised as humans who see children as disposable fodder for their perversions. We are then surprised when they grow up into criminals.

Most insidious of all, the old public attitude that all adults are responsible for all children has gone. Most people don't even see anything shorter than 4ft 6in tall, unless they're being annoyed by it.

Why should mothers take the blame? It's ridiculous that shops are designed by men for use mainly by mothers with children. It doesn't take genius to think of simple things that would help to reduce danger - only a bit of experience with a toddler.

All shopping precincts should have creches. There is an enormous place near me where I go every couple of weeks: it is inconvenient to reach, often crowded and rather expensive; but I go there solely because it has a creche. Not everyone can afford its fees: yet considering their mark-ups, I think shops could afford to subsidise it.

Shops with open doorways could station staff at the entrance to watch out not only for shoplifters but for escaping children. Shops could also reduce the hassle: they could stop deliberately confusing us with their flow-science to make us buy more; and they could all have packers to sort out purchases, and no sweetie display.

How about some new technology - two lockable bracelets, one for the mother and one for the child? If the child wanders more than (say) 20ft from the mother, his bracelet activates a warning alarm. What about automatic doors that don't open for unaccompanied children?

In the meantime every mother carries on having nightmares every time she goes out with her children.