His speech was given at a joint conference of the American Advertising Federation, the American Association of Advertising Agencies and the Association of National Advertisers.
Harkin made it clear to the advertisers that if they did nothing to reduce or even stop advertising to children, then the only way forward would be to instigate legislation.
"When it comes to the advertising and marketing of food to children, it is still my hope that real restraint will come from within your industry...obviating the need for further federal regulation," he said.
It is well documented that America is in the grip of an obesity crisis, Harkin said that 15 percent of American children and teenagers are obese, "a higher rate than in any other industrialized country". However, he said that there was added urgency to do something with new evidence that today's young generation could be the first to suffer a shorter lifespan than the one that preceded it.
"The alarms are going off, one after another. Yet, we keep hitting the snooze button."
He said that inactivity and poor nutrition were together contributing to the obesity crisis, but that children were consuming more calories and more foods high in sugar, fat, and salt because they taste good, are available everywhere and are "being aggressively advertised and marketed".
He added : "Corporate America...spends $12 billion [on advertising aimed at children] because that advertising works brilliantly because it persuades children to demand - to the point of throwing temper tantrums, if necessary - a regular diet of candy, cookies, sugary cereal, sodas, and all manner of junk food".
Children under the age of eight are unable to tell the difference between a TV program and a commercial and parents should not have to sit there watching children's shows to check whether there are any offending ads, said Harkin.
"Not even schools are safe havens anymore. There is Channel One, with ads for candy bars and sugary sodas. There are giant Coke machines that double as billboards, right in the school hallway or cafeteria."
He cited a Wall Street Journal poll from February that had found that 68 percent of American adults believe that advertising to kids is a major contributor to the rising tide of obesity in children and that a clear majority said government should do more to regulate food ads directed at children.
Stephanie Childs from the Grocery Manufacturers of America recently told FoodNavigatorUSA.com that she believed that most food companies practised responsible advertising that complies with the Children's Advertising Review Unit (CARU), meaning that, for example, if a snack is being advertised the "right size serving is shown in the right context".
Harkin admitted that the "CARU has done some good things" and was at least an acknowledgement by the advertising industry that irresponsible food marketing to children is a very real problem, but he did not think that it went far enough.
"CARU is not cutting it. It has no legal authority - and it has no teeth."
Harkin wants the advertising industry to sit down with the food and broadcasting companies to "hammer out tough, rigorous, age-appropriate standards to govern the marketing of junk food to children. And create an enforcement body that has independence and teeth."
The senator had already announced last month that he planned to propose a bill enabling the FTC to regulate food advertising to children.
"The Harkin bill would restore the FTC's power to regulate advertising for children - taken away during the cavity epidemic of the 1980s to save food companies from suffering restrications - but it would be up to the FTC to decide how and what to regulate," Allison Dobson, Harkin's spokeswoman, explained to FoodNavigatorUSA.com.
She added at the time that Harkin also planned to table a second bill, which would allow the secretary of agriculture to prohibit junk food advertising in schools.
The ban on food advertising to children is a stance supported by the Center for Science in the Public Interest (CSPI) that has already drawn up guidelines suggesting that only "products that may not be nutritionally ideal but that provide some positive nutritional benefit and that could help children meet the dietary guidelines" should be advertised to children.
"Companies should not conduct general brand marketing aimed at children for brands under which more than half of the products are of poor nutritional quality," believes the organization.
Michael Jacobson, executive director of the CSPI, added: "Ideally the food manufacturers should limit their advertising, but they can't control themselves. Therefore, it will fall to government to come up with some rules".
The GMA, on the other hand, naturally takes a less rigid approach, affirming that steps are already in place to make sure children see only the right sort of advertising and thinks it is nonsense to suggest children upto the age of 18 need to be protected from food advertising.
"We do not support a ban on advertising food products. A ban would not be the right solution," said Childs. Instead, she said that the organization would be looking at what is working in then present system and building on that.
Dobson admitted that there were ongoing improvements in the food industry, but felt they were "small steps". "If they had happened 10 years ago they might have brought us somewhere," she said, adding that more drastic action is needed.
The GMA, however, believes that the food industry is taking huge steps forward. "GMA members have introduced thousands of new and reformulated products that are lower in saturated and trans fats, sodium and sugar," said Manly Molpus, CEO of the GMA.