Researchers found that shortly after playing a game with an embedded food advertisement, children ate 55 percent more of the candy offered to them than children who had played a game with an embedded toy advertisement.
At least once a week, two thirds of all children of primary-school age will play an internet game that was created to draw attention to a brand, researchers said.
Most of these advertisements are for snacks and candy. Only 6 percent of these children are aware that such advergames are advertisements.
Such games do affect their behaviour, said Frans Folkvord, from Radboud University in The Netherlands.
Folkvord tested the effects of such hidden online food advertisements on the eating behaviour of more than 1,000 children.
"In contrast to television, where the clearly delimited blocks of commercials can help viewers guard against temptation, on the internet, advertising is mixed with other types of content," said Folkvord.
"The websites of food manufacturers contain games, which also offer children the option of sharing games with their friends," he said.
Folkvord found that children do not recognise the games as advertisements, even when brand names and logos are clearly visible.
Moreover, it does not matter whether the games are about candy or fruit - children eat more candy after playing a game involving food.
During the five-minute break after playing the food-related games, children ate 72 more calories than did children in the control conditions.
Although Folkvord found no link between eating candy and having a higher BMI two years later, choosing the snack did have an effect.
The BMIs of children who chose to satisfy their hunger with an apple instead of with candy were lower two years later than were those of children who had chosen to satisfy their hunger with candy.
"These children had apparently learned to make healthier choices," Folkvord said.
"Children play a game, get hungry and reach for treats. As the cycle continues, children fail to learn healthy eating behaviour," said Folkvord.
"The results of my study indicate that these advertisements have an even heavier influence on children who are already overweight," he said.
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