Should manufacturers of so-called “low-nutrition” foods be allowed to market their products to children? The answer, according to many food scolds is no.

The Institute of Medicine — a private group with funding from the Center for Disease Control — held hearings in Washington, D.C. recently to ask various food industry executives why they are marketing harmful products to children. This came on the heels of a media blitz by the lofty-sounding Center for Science in the Public Interest, which issued a plan calling for restrictions of junk food, including a complete ban on cross-promotional campaigns – think SpongeBob SquarePants Cereal.

“Ideally,” the CSPI press release proclaimed, “only healthful foods like fruits, vegetables, and whole-grain products would be marketed to kids.”

Even if we set free speech concerns to the side, ad bans make for bad public policy for a number of reasons.

Ad bans have failed everywhere they’ve been tried. The list so far includes Sweden, Quebec, and Norway. None of these places have shown significant reductions in child obesity. In Sweden, the restrictions have been in place for a decade, yet the country’s childhood obesity rates are in line with the rest of Europe.

There’s no correlation between ad exposure and childhood obesity. George Mason University’s Todd Zywicki noted at a forum last summer that the average American child actually watches less TV than he did 15 years ago. What’s more, children face less exposure to food ads now than they did then, for a variety of reasons. The remote control has made ad-watching optional over the last 20 years, and more recent technology like TiVo may make traditional commercials completely obsolete.

Broadcast television is also losing younger viewers to cable, where ads in general are 40 percent less prevalent and where food ads comprise about half the percentage of overall ad time that they do in broadcast. Cable also offers more options for channel-flipping during commercials, and premium cable stations like HBO, which have no commercials at all, have become popular. All told, the average American child viewed 900 fewer food commercials in 2003 than he did in 1994. That this same average child gained weight amounts to a pretty solid rebuttal to the theory that food marketing is a significant contributor to childhood obesity.

You’d need to ban ads in adult programming. The fact is, you simply can’t limit a kid’s exposure to food ads, unless you’re prepared to ban all food advertising. Most children’s television viewing isn’t limited to children’s television programming. Kids watch shows intended for adults, too.

In fact, the kids most prone to obesity – those with minimal parental supervision – are also very likely those most likely to watch adult programming. Former Federal Trade Commission administrator Timothy Muris pointed out in a conference last June that if Congress had caved and banned food ads aimed at kids the first time the idea was proposed in the 1970s, the only television show that would have been affected would have been Captain Kangaroo.

Today, such a ban would probably hit a few other programs as well, which brings us to the next point…

The ban would cripple children’s television. The FCC already mandates that broadcasters devote a portion of the broadcast day to children’s programming. Food ads make up a huge portion of the ad revenue for those programs. Cut off that ad revenue, and the broadcasters subject to FCC regulation lose any incentive to invest in high-quality children’s television. Why put money into a sure loser?

Furthermore, television not subject to FCC regulations — cable, for example — would likely drastically cut back on the amount of television time it carves out for children, or just disregard children’s programming entirely.

The cause of childhood obesity lies elsewhere. Several recent studies have suggested that the single best indicator of a child’s health, diet, weight, and activity level is the health, diet, weight, and activity level of that child’s parents. Children of active parents tend to be active. Kids tend to eat what their moms and dads eat.

That said, there’s also some evidence that the caloric intake among kids hasn’t changed much over the last quarter century. What has changed is the amount of time kids are active, outside, and exercising. Kids today may watch less television, but they more than make up for it with video games, Internet activity, DVDs, or some combination of the three.

Holding Tony the Tiger, the Nabisco elves, or SpongeBob responsible for childhood obesity is certainly the easiest public policy prescription for childhood obesity. It would be much more difficult, and perilous, to charge parents with neglect or child abuse for allowing their kids to get dangerously fat.

But ultimately a child’s diet and exercise habits do begin with his parents. The food industry can’t be faulted for putting products on the shelves that sell, nor can it be faulted for marketing those products to the people who will pester their parents to buy them.