Children who spend more than half an hour online a day are almost twice as likely to bug their parents for junk food, a study recently found.

Researchers at the University of Liverpool looked into the link between diet and junk food advertising on TV and online, asking 2,500 7-11-year-old children and their parents about their eating habits and screen time (outside of homework).

Children who perused the web for at least three hours a day were more than four times as likely to spend their pocket money sweets, chips and sugary drinks as opposed to kids to spent less than half an hour online. These children were also 79 percent more likely to be overweight or obese while those who were online between 30 minutes and three hours a day were 53 percent more likely to be carrying excess weight than those who were online for less.

"Our research shows that this behavior can be linked to the amount of time children spend in front of a screen and as a result, the increased number of enticing adverts they see for these sorts of products," researchers concluded.

On average, children were online for 16 hours a week -- not including time spent for homework -- and watched 22 hours of television per week, the study found. Each additional hour of commercial TV that children watched was linked with an increased likelihood of pestering their parents to buy products they had seen advertised.