When Katherine Kim of Ellicott City goes grocery shopping with her 4-year-old son Jonathan, she keeps any whining and food requests to a minimum by telling him in advance what they're going to buy. She typically picks up ice cream last, giving Jonathan something to look forward to as their shopping cart glides past shelves stuffed with cookies, potato chips and sweet cereals.

Still, she said, Jonathan is partial to Kraft Macaroni & Cheese shaped like characters in the "SpongeBob" television show or "Cars" movies. She'll sometimes buy the boxes he requests, she said, describing the indulgence as relatively harmless.

"There are a lot of commercials out there," she said, loading groceries into her car in the Safeway parking lot, as Jonathan sang a happy song about the newly purchased ice cream.

Nobody said grocery shopping with preschoolers would be easy. But a new research paper from Johns Hopkins says television commercials and cartoon-covered packaging make it more difficult than it has to be, prompting children to beg their parents for foods that are not necessarily good for them.

Dina Borzekowski, the mother of children ages 14, 10 and 6, is also a researcher, and she has tackled the questions of how children beg for treats, and how adults respond to that begging, in a research paper titled "The Nag Factor."

"We know that advertising has an impact on children, and we know there's a relationship between media use and obesity, but when you look at little kids, they're not the ones doing the shopping," said Borzekowski, an associate professor with the department of health, behavior and society at Hopkins' Bloomberg School of Public Health. She collaborated with doctoral candidate Holly Henry on the study, published in the August issue of the Journal of Children and Media.

Undaunted by fears of mortality or obesity, youngsters see no reason to choose a nutrient-rich diet over one dense in sugar, fat and sodium. Add some television commercials and packaging decorated with cartoon characters, and a stroll through the cereal or snack aisle can become a test of wills, as children beg for treats and exhausted parents make moment-by-moment decisions on when to give in and when to say no.

"Mothers described packaging, characters, and commercials as the three main forces compelling their children to nag," said the report.

The study looked at the techniques children use to beg for food, and the strategies parents use to cope with the begging. The researchers interviewed 64 mothers of children between the ages of 3 and 5 from Maryland and D.C., recruited mostly through day care centers and neighborhood listserv mailing lists. The mothers were interviewed one on one, with no children present, in locations of their choosing, such as coffee shops.

The researchers decided to limit the study to mothers and exclude fathers, on the theory that fathers bring an entirely different set of standards and rules to the experience of supermarket shopping with youngsters.

"We actually feel that there's a difference between how moms shop for food and the way dads shop," Borzekowski said. "There seems to be a return to childhood when dads go to the supermarket," with dads more willing to purchase treats that moms would reject.

She quickly added: "That's not a professional opinion."

So the moms were given the chance to talk, and apparently they had a lot to say on the topic. Most interviews lasted at least 45 minutes, Borzekowski said, and some moms described their food-related frustrations and philosophies for as long as an hour and a half. "Every mom has a story about the tantrum in the cereal aisle," said Borzekowski.

Borzekowski said the study, conducted in 2006 and 2007, is merely a first look at the strategies used by children to beg for food, and by parents to deflect the bombardment.

The study found a difference between the way 3-year-olds beg for treats and the strategies used by children who are 4 or 5. The younger children are more likely to whine and pull on a pants leg, Borzekowski said, while the older ones will offer fairly sophisticated arguments, even promising to do chores in exchange for the items they want.

Also of note was that even children with limited exposure to television recognize characters such as SpongeBob and Dora the Explorer because the licensed characters are so ubiquitous. "As a parent, that makes it really hard," Borzekowski said.

The study identified 10 techniques used by parents: giving in, yelling, ignoring, distracting, limiting exposure to commercials, shopping without children, setting rules, explaining, offering alternate items, and giving firm and calm responses.

Clearly, some of these strategies are more desirable than others.

"It is really hard to say no," acknowledged Jenny O'Grady, who lives in Timonium and is the mother to Max, 3. The strategy in her house, she said, is to limit exposure to television commercials. "So far, it's going pretty well," she said. "He definitely doesn't know any names of brands," she added, and he eats oatmeal instead of sweet "kid" cereals.

The family snacks on fruit and ice pops as sweet treats, and when they go shopping, O'Grady asks Max for help choosing which fruit to buy. Though he likes characters such as Dora the Explorer, he has not expressed a preference for foods with those characters on the packaging, she said. Dora can be found on Yoplait yogurts and Spaghetti-Os.

Borzekowski sees plenty of room for future research. She points out the mothers in the study were disproportionately well-off and well-educated, and "we know that kids who grow up in households that have less education are actually more vulnerable to more media use and more obesity," she said. Subsequent research should focus on families at lower income levels and with less education, she said.

But the bigger question is the one that parents always seem to ask themselves: What to do?

"I'd love to do the follow-up at looking at which strategies work," Borzekowski said.