(CNN) Snack commercials that kids see on television may be more persuasive than you might think.
The food advertisements that children as young as preschool age view while watching their favorite shows can sway them to overeat even when they're not hungry, a new study suggests.
The small study, which was published in the journal Pediatrics on Monday, is the first of its kind to weigh the effect that food advertisements have on preschoolers' snacking habits, said Jennifer Emond, lead author of the study and an assistant professor in the Geisel School of Medicine at Dartmouth College.
Until now, most studies have examined that effect among school-age or older children. Yet "highly palatable, unhealthy foods are heavily advertised to kids as young as 2 -- primarily on TV," Emond said.
"Overall, our research suggests that exposure to food ads can prime eating behaviors in young children that tells children to respond to external signals instead of listening to their own internal signals of fullness and hunger," she said. "That learned response may set children up for developing poor eating habits that contribute to obesity."
The study involved 60 children, ages 2 to 5 years old, who were shown a 14-minute segment of "Elmo's World" from the show "Sesame Street." Half of the children watched the segment embedded with a mix of food advertisements, while others watched the segment embedded with a mix of department store ads.
Before viewing, all of the children were provided with snacks to eat and were surveyed on how hungry they felt.
Then, while viewing the segment, the children were provided with two snacks: corn snacks and graham snacks. The same corn snacks provided were featured in the food advertisements shown to some of the children.
The researchers found that the preschoolers who watched the segment embedded with food ads consumed more calories in snacks on average than those who watched the department store ads.
Additionally, the children who watched the food ads ended up eating more of the advertised corn snack than the graham snack -- even if they had never eaten the corn snack before and, therefore, were not familiar with it.
"That was surprising because it demonstrated the powerful effect food advertising can have on priming potentially unhealthy eating behaviors at a young age," Emond said.
Emond added that similar findings have been demonstrated among older children in separate studies.
The researchers believe that this latest finding among preschoolers could be replicated in a larger sample size.
"Given the consistency in the findings across different studies and now among different age groups, we do think we are measuring a true effect," Emond said.
Why might food advertisements have this effect on preschoolers? More research is needed to find a clear answer.
However, it might have something to do with a reward system in the brain called the dopaminergic mesolimbic pathway, according to a study published last month in the International Journal of Obesity.
In that study, which involved about 200 children ages 9 to 10 years old, the researchers wrote that tasty snacks are known to activate that reward system in the brain.
Further research is needed to explore whether "seeing food cues in advertisements unconsciously signals children to eat in order to feel that rewarding sensation," Emond said. "Importantly, we also know from our previous research that some children may have a genetic predisposition to respond to food ads."
About 40% of all food and beverage ads that children and teens see on television are for unhealthy snacks, according to a 2015 report by the University of Connecticut's Rudd Center for Food Policy and Obesity (PDF).
"Parents should not shrug off food marketing. These ads really do influence children," said Marlene Schwartz, director for the center and a professor of human development and family studies at the University of Connecticut, who was not involved in the new study.
"If the ads were for healthy foods, that would be an asset to parents, but when the ads are for unhealthy foods, they make parents' job harder," she said.
Indeed, food ads can be successful in encouraging healthy snacking, too.
It turns out that marketing healthy foods in the same way as unhealthy snacks can nearly triple the likelihood of a child munching on fruits and vegetables, according to a study published in the journal Pediatrics this year.
"There is no doubt that advertising affects children. But we should also recognize that everyone -- children, adolescents and adults -- are exposed to media of all sorts on a daily basis," said Andrew Hanks, assistant professor of human sciences at Ohio State University and lead author of that marketing study.
"The more parents know about the impacts of advertising on children, the more they can help their children prepare to process the messages in an appropriate manner," he said. "If parents are going to make food readily available for their children, choose the lower-calorie snacks, such as cut-up apples or carrot sticks."
Many children's television programs are now offered ad-free through various services, said David Just, a professor at Cornell University who was a co-author of the same marketing study as Hanks.
"We think it is very important for parents to understand the impact that advertising of any kind has on their children," he said. "Also, it is important for parents to be aware of what their children are watching and the types of ads their kids are viewing. And not only to be aware but to talk to them about what they see."