Portuguese children are having less exercise and will become fatter as a result, especially the poorer ones.
Researchers at the University of Coimbra say the shocking results require government intervention to avoid problems of obesity and associated disease later in life.
Between 2002 and 2009 the number of kids watching more than two hours of TV a day increased 12% on weekdays, 15% on Saturdays and 17% on Sundays.
One of the reasons for this increasingly sedentary lifestyle is the Magellan computer that was handed out to school children to encourage web-based education.
In 2002 poorer children hardly used computers but in 2009 around 19% of children spent over two hours a day on the computer, according to the Coimbra research complied by Cristina Padez at the Research Centre for Anthropology and Health.
The study compared the habits of 9,032 Portuguese children between 2002 and 2009 and was presented at the International Society of Behavioural Nutrition and Physical Activity conference in Edinburgh.
"Children whose parents have low levels of education are the ones who spend more time watching television," said Cristina Padez, stressing that, with regard to computer use, "the situation worsens."
With regard to sporting activities after school finishes for the day, the survey revealed that "only half of the children are having any physical activity out of school. In lower socio-economic levels, the percentage of children who do not practice sport went from 36% in 2002 to 80% in 2009."
Padez concluded that "policymakers should create a strategy to combat sedentary lifestyles in children, otherwise we will have adults with serious health problems with very high socio-economic costs."
