When Susan Connor's 3-year-old son started humming the McDonald's jingle, a research project was born.
Connor knew where he'd heard the fast-food giant's catchy tune — on the Disney Channel during "The Wiggles," a show for preschoolers.
"He had absorbed that from watching TV," said Connor, whose study on food ads aimed at toddlers appears in the October issue of Pediatrics. "It would be a marketer's dream to know they were that successful."
Messages for high-fat, high-sugar foods permeate programming for preschoolers on Nickelodeon, the study found. On the Disney Channel's shows for the youngest children and even on Public Broadcasting Service shows such as "Sesame Street," companies woo tots' loyalty by linking logos, licensed characters and slogans with fun and happiness.
Disney and PBS promote themselves as ad-free, but fast-food companies dominated sponsor messages during programming for toddlers, Connor found, making up 82 percent of sponsor messages on PBS preschool programming and 36 percent of messages on Disney's toddler block of shows.
The clown character Ronald McDonald appears with shows for toddlers on Disney and PBS. The cartoon mouse Chuck E. Cheese pops up alongside preschool programming on PBS.
Connor, research manager of Cleveland's Rainbow Babies & Children's Hospital, said adults who haven't seen children's programs lately will be surprised by the findings.
Advocates said the study adds to mounting evidence that food marketers are trying to hook the youngest children as lifelong customers. Promotions go both ways with TV characters from children's shows used on the packaging of sugary cereals, fruit-flavored snacks and other foods.
Last week, the Federal Communications Commission announced plans to study links between the ads, viewing habits and the rise of childhood obesity. For now, marketing of food to children is unregulated.
Previous studies have found that kids as young as 3 who see TV ads are more likely to request and eat advertised foods high in fat, sodium and sugar. American children from infancy to age 6 watch an average of one hour of TV daily, and 8- to-18-year-olds watch an average of three hours daily. They see roughly 40,000 TV ads a year.
"It's very concerning when childhood obesity is a major public health problem that preschool programs are still being sponsored by fast food restaurants and food that's not healthy for children," said Susan Linn of Harvard Medical School and a co-founder of the Campaign for a Commercial-Free Childhood. She was not involved in the study.
Diane Levin of Wheelock College, who is also a co-founder of the Campaign for a Commercial-Free Childhood, criticized Disney and PBS for breaching viewers' trust. She supports limits on marketing of junk food to children too young to make critical judgments about advertising.
"PBS has a special responsibility," said Levin, who was not involved in the study. With federal funding threatened, Levin said, PBS has searched for new revenue, including money from sponsors who want to reach children.
PBS spokeswoman Lea Sloan said sponsors' messages don't interrupt programs and don't go longer than two minutes, 17 seconds per hour. PBS doesn't allow price information, product comparisons, depictions of children's products or superlative claims, Sloan said.
"The content of these messages is either in support of public television or around learning, education and social development," Sloan said in an e-mail. "Licensed characters or mascots often reinforce a positive educational message and their appearance is limited to five seconds."
Nickelodeon spokesman Dan Martinsen said the channel has reduced food ads during its "Nick Jr." block of programs for preschoolers by 20 percent in the last two years.
Disney Channel spokeswoman Patti McTeague said sponsor messages are accepted "only when they are connected to a pro-social message."
Chuck E. Cheese spokeswoman Brenda Holloway said the pizza restaurant chain's play areas promote physical activity, as do its ads.
"Realistically, our research shows most children come to Chuck E. Cheese's to play and have fun," Holloway wrote in an e-mail. "We think that our PBS sponsorship announcements do promote physical activity and social interaction through play and learning, which we believe are appropriate messages for preschool-age children."
McDonald's did not respond to requests for comment in time for publication.