Adverts for sugary foods and drinks causes children to want to impulsively have tasty food that is "bad" for them, a new study warned.
Marketing promotes the hedonic aspect of eating by activating their brain's reward centre just after watching an advert.
So when it comes to what to eat, they put taste above health and decide quicker on what they want.
It is estimates American children watch 1,000 adverts and teenagers over 2,000 in a year and their eating habits are being driven by the multi-billion dollar industry
The US investigation on how commercials influence children's food choices suggested firms are not wasting their money.
Assistant Professor in behavioural paediatrics Dr Amanda Bruce at the University of Kansas Medical Centre said: "Food marketing is cited as a significant environmental factor implicated in food choices, overeating, and ultimately, obesity.
"Television advertising and branding have an effect on both food familiarity and preference.
"Research examining the effects of television food advertising on children has shown that children exposed to advertisements prefer branded foods at much greater rates
than children not similarly exposed.
"Television advertising impacts food consumption and eating behaviours as well.
"Behavioural studies have documented the relationship between receptivity to food commercials and the amount of food consumed.
"For example, snack and sweet food intake increases during or after commercial viewing in children.
"Children who are overweight may be more responsive to food branding and therefore at greater risk for marketing persuasion."
She added research suggested a link between marketing for unhealthy foods and increased childhood obesity.
The study involved 23 children aged eight to 14 who rated 60 food items on how healthy or tasty they were.
Their brains were then scanned while watching food and non-food commercials.
Prof Bruce said: "We hypothesised that food commercials would bias the children to make more taste-oriented choices.
"For brain analyses, our primary focus was on the brain region most active during reward valuation-the ventromedial prefrontal cortex (vmPFC).
"We hypothesised that, after the children viewed food commercials, activity in their vmPFC would increase while they made specific food choices."
During the brain scan, children were asked whether they wanted to eat the food items that were shown immediately after the commercials.
Results found overall, the children's decisions were driven by tastiness rather than healthfulness.
Prof Bruce added : "Our results showed that watching food commercials changed
the way children assess the importance of taste when making food choices.
"Children placed significantly more importance on taste after watching food commercials compared with non-food commercials.
"It is possible that the food commercials prime children to focus on the more hedonic aspects of food.
"Food commercials may prompt children to consider their liking and wanting of specific food items, irrespective of the lack of any health benefits.
"This increased emphasis on taste may make it even more difficult for relevant caregivers to encourage healthy food choices."
They were also quicker to make up their mind whether they wanted to eat the food item after watching food commercials.
Additionally vmPFC of the children were significantly more active after watching food commercials.
She added: "Overall, our results suggest watching food commercials before making food choices may bias children's decisions based solely on taste, and that food marketing may systematically alter the psychological and neurobiologic mechanisms of children's food decisions."
The study was published in The Journal of Pediatrics.