Which? researchers kept track of the marketing techniques of 12 food companies -- Burger King, McDonald's, KFC, Coca-Cola, PepsiCo, Cadbury-Schweppes, Haribo, Kellogg's, Kraft, Masterfoods, Nestle and Weetabix -- for six months, and interviewed roughly 50 children prior to the publication of their report.
The researchers found that the most popular marketing tactic, "viral marketing," uses the internet to encourage children to email branded messages to each other. Other techniques use children's films, the World Cup or competitions to attract children.
Which? researcher Nick Stace said advertisers are also targeting parents in an attempt to make junk foods high in salt, sugar and fat seem like healthy options for their children.
"How can parents be expected to give their children a healthy, balanced diet when these sophisticated, underhand techniques are targeting their children, often behind their backs?" Stace said. "Most of [junk food companies'] so-called responsible marketing policies are simply empty rhetoric."
UK ad regulator OFCOM announced two weeks ago that it would enforce a ban on junk food ads during TV programs targeted at children younger than 16 years old, as well as a complete ban on junk food ads on children's channels and children's programs on adult channels watched by many children.
However, Which? says OFCOM's new regulations do not go far enough to protect children, and a complete ban on all junk food ads on all channels should be enforced before the 9 p.m. watershed.
The food industry has condemned the Which? report, claiming it is actively working with the government to safely advertise to children.
Kellogg's spokesman Chris Wermann called the report "sensational ... selective, ill-informed and unrepresentative." McDonald's issued a statement claiming it does not engage in "underhand" marketing and does not market junk food to children.
Jenni MacDougall of Cancer Research UK said, "The techniques used to promote foods high in fat, salt and sugar are very creative, and many of them hold appeal for children. With childhood obesity reaching alarming levels, it is vital that the problem is tackled from all angles.
"We are disappointed that OFCOM has not gone further in its proposals to restrict junk food advertising to children," she said.