The foods marketed by these two companies are "directly harming kids' health," claim two parents together with pressure groups Center for Science in the Public Interest (CSPI) and the Campaign for Commercial-Free Childhood, who are filing the lawsuit.
A Massachusetts court will be asked to prohibit the companies from marketing junk foods to audiences made up of over 15 percent of under eight year-olds, as well as using certain techniques targeted at the age group to market these foods, such as websites, toy giveaways and contests.
This is not the first time the food industry has come under attack for this issue. With childhood obesity becoming a growing problem in the US, the nation's food and soft drinks industry has been under increasing consumer and political pressure in recent years to reduce the promotion and marketing of junk food to children.
Indeed, last year, Senator Tom Harkin sent a strong message to the food industry, saying that it must move swiftly to stop the advertising aimed at children that was creating a "botched" generation.
In a speech given at a joint conference of the American Advertising Federation, the American Association of Advertising Agencies and the Association of National Advertisers, he made it clear to advertisers that if they did nothing to reduce or even stop advertising to children, then the only way forward would be to instigate legislation.
And according to a study conducted last year by researchers at the University of Illinois, nutrient-poor high-sugar products dominate television advertising aimed at children between the ages of 6 to 11.
Overall about 78 per cent of the food advertised during TV programs watched by young children is junk food, with publicity for candy, sweets and soft drinks making up 44 per cent of the total.
And 'junk', which is the general term used for food that is described as nutritionally deficient and high in calories, is what Kellogg and Viacom, parent company of Nickelodeon, are now accused of marketing to children.
According to the CSPI, the "overwhelming majority of food products they market to children are high in sugar, saturated fat, or salt, or almost devoid of nutrients."
"Nickelodeon and Kellogg engage in business practices that literally sicken our children. Their marketing tactics are designed to convince kids that everything they hear from their parents about food is wrong. It's a multimedia brainwashing and re-education campaign- and a disease-promoting one at that. And parents are fed up." said CSPI executive director Michael Jacobson.
The claims are being made on the basis of the CSPI's review and analysis of the two companies' marketing methods, which, according to the group, use well-loved cartoon characters and "kid-friendly" websites and packaging to promote "nutritionally poor" foods.
And plaintiff parent Sherri Carlson agreed that "all those enticing junk-food ads" make her children want to eat "junky snacks and cereals" instead of "healthy foods."
"This irresponsible marketing to young children undermines my efforts as a parent and must be stopped," she said.
"For over thirty years, public health advocates have urged companies to stop marketing junk food to children," added Susan Linn, co-founder of the Campaign for a Commercial-Free Childhood.
"Even as rates of childhood obesity have soared, neither Viacom nor Kellogg has listened. We can no longer stand by as our children's health is sacrificed for corporate profits," she added.
The CSPI cited food giant Kraft as a company that has set nutritional guidelines for the foods it markets to children, and one that does not market to children under the age of six.
Indeed, last year Kraft announced its new advertising policy for children, due to be implemented by the end of 2006, which aims to modify product marketing on its websites aimed at children to include only products that meet its Sensible Solution nutrition standards.
The CSPI conceded that "Nickelodeon has engaged in public relations activities on the issue of childhood nutrition, notably a promise to make SpongeBob and other characters available to marketers of some healthful foods," but added that "it hasn't set minimum nutrition thresholds for the foods its characters plug or that run on its station."
If Kellogg and Viacom go to trial and are found liable, the CSPI said the plaintiffs would "settle for a commitment from the companies to change their marketing practices."