With spring in the air, my thoughts naturally turn to helmets. I don't think I knew anyone who wore a bicycle helmet when I was growing up. My older brother gave me one when I was a teenager because I rode my bike to school every day. I wore it once and was so mercilessly ridiculed ("Luke Skywalker" was one of the kinder epithets) that I stashed it in a closet and never put it on again.

Sixteen years later, I bought my daughter her first two-wheeler at a bicycle store in Manhattan. Although I knew that a sea change had occurred in public attitudes regarding bicycle helmets, I did not initially plan to get one, since we were buying a little bike with training wheels that Francine would be riding on the sidewalk at a speed barely faster than she could walk.

But the salesman explained that wearing a bicycle helmet was no longer just a good idea. For bicyclists younger than 14 in New York State, no matter how poky or closely supervised they were, it was also the law.

I understand, of course, that We Know More Now than we did 20 or 30 years ago, when parents blithely allowed their children to ride bikes on all sorts of terrain at any speed with their noggins completely unprotected. I also understand that children can be seriously injured even at low speeds; my wife knows of a family whose 3-year-old son died of a head injury in a freak tricycle accident.

Since risk can never be completely eliminated, however, the question is not whether your child conceivably could be killed while engaging in a particular activity. It's how likely such an outcome is and whether the risk is acceptable.

The first part can be answered more or less objectively, based on accident statistics. But the second part depends on value judgments that cannot be definitively proven right or wrong.

Obviously, the surest way to avoid bicycle injuries is to avoid bicycles, but most of us would not insist that parents go that far, because biking has benefits that are widely believed to outweigh its dangers. By contrast, to allow your kid to ride a bike without a helmet--the universal practice until relatively recently--is now seen as a form of child neglect.

Parents today are not just more aware of risk; they're less tolerant of it. Rising affluence, declining birth rates, and the tendency to have children later in life have made us more anxious about our offspring. There's no reversing this trend, but perhaps we should reflect a little on how far we want it to take us.

Last January, for example, the New York City Council approved an ordinance requiring helmets for children riding scooters. Perhaps the sudden popularity of scooters made such legislation inevitable. But this mandate sets the threshold for acceptable risk awfully low.

Although scooter sales went from nearly zero in 1999 to several million in 2000, the Consumer Product Safety Commission counted only two scooter deaths last year. The number of bicycle fatalities each year is almost 500 times as high, while the number of Americans who ride bikes (something like 50 million annually) is only about10 times the number who rode scooters last year. In other words, scooting appears to be much less risky than biking.

Seduced by a misleading analogy between scooters and bicycles, politicians meanwhile overlook far more serious hazards. Children suffer almost as many head injuries while using playground equipment, for instance, as they do while riding bikes.

And what about sledding? It hardly seems reasonable that Francine must wear a helmet while pushing herself along the sidewalk on her scooter but not while careering down a snow-covered hill on a plastic disk.

Rather than requiring helmets in every situation where children could hurt their heads, perhaps we should admit that such mandates carry a cost we are not always willing to bear. The cost goes beyond the price of a helmet; it is also measured in discomfort, inconvenience, and a loss of spontaneity.

At the margin, a helmet mandate may mean less exercise and more TV or PlayStation at a time when kids are fatter and less active than ever. It definitely means that parents must cede a little bit more of their authority to determine what is best for their children--an area where the state should tread less casually.