Food ads influence what children want to eat but healthy messages from parents may help to temper the influence, researchers have found.

In the experiment, children were allowed to choose a coupon for apple slices or french fries that they saw advertised during cartoons.

The parents were randomly assigned to follow a script that advised the children to select the healthier food or the food the child wanted the most.

Among the children who saw the commercial for fries, 71 per cent chose the coupon for french fries if their parents remained neutral, compared with 55 per cent who opted for the fries coupon if their parents encouraged them to choose the healthy food.

"Children were clearly influenced by the commercials they saw; however, parents are not powerless," said study author Dr. Christopher Ferguson of Texas A&M International University.

"Parents have an advantage if they are consistent with their long-term messages about healthy eating," he added in a release.

Among the children who saw the commercial for apple slices, 46 per cent chose the coupon for french fries if their parents were neutral, while 33 per cent picked the coupon for fries if their parents encouraged them to choose the apple slices.

Parents said their children watched at least three hours of TV a day on average. Given this relatively frequent amount, the potential impact on healthy eating and the potential for obesity "probably should not be ignored," the study's authors said.

Watching TV was not predictive of children's excess weight, and the researchers acknowledged the finding was based on a very small sample and should be interpreted with caution.

The sample of 75 families included mainly Hispanics, so the findings may not apply across the board, the researchers said.

"Food advertisements directed at children may have a small but meaningful effect on their healthy food choices," Ferguson's team concluded.