Children spend so much time in front of television and computer screens, they are at risk of developing an addiction to them, according to a leading psychologist.
Dr Aric Sigman said that allowing children too much time in front of a screen amounted to a form of "benign neglect" by parents.
He said: "Passive parenting in the face of the new media environment is a form of benign neglect and not in the best interests of children. Parents must regain control of their own households."
The average screen time for young British adolescents is now 6.1 hours a day and rising.
Ten to 11-year-olds now have access to an average of five screens at home, often using more than one type of screen at the same time, such as texting while watching TV.
And by the age of seven, a child born today will have spent one full year of 24-hour days watching screen media, Dr Sigman will tell doctors today at the annual conference of the Royal College of Paediatrics and Child Health in Glasgow.
Even average levels of daily screen viewing are strongly linked to a significantly increased risk of type 2 diabetes, heart disease and early death.
But he will warn that high levels of screen exposure early in childhood appears to increase the chances of developing a long-term habit of overuse and in some cases, even addiction. He said there are now concerns that extensive computer game playing in children may lead to long-term changes in the brain's reward circuitry that resemble the effects of substance dependence.
Parents are often unaware of how their own behaviour influences their children's use of technology. If parents watch television for more than four hours per day, their son is 10.5 times and their daughter is three times more likely to watch more than four hours per day too, Dr Sigman said.
And parents who maintain high levels of eye-to-screen contact while using smartphones at home are likely to encourage similar behaviour in their children.
Dr Sigman said: "Technology should be a tool, not a burden or a health risk.
"Whether children or adults are formally 'addicted' to screen technology or not, many of them overuse technology and have developed an unhealthy dependency on it.
"While there are obviously a variety of different factors which may contribute to the development of a dependency - whether it involves substances or activities - the age, frequency, amount of exposure along with the ease of access and the effects of role modelling and social learning, all strongly increase the risk.
"All of these contribute to a total daily exposure to, or 'consumption of', an activity. And all are prerequisite factors that contribute to the risk of dependent overuse of technology."
Terence Stephenson, President of the Royal College of Paediatrics and Child Health, said: "Children are becoming increasingly younger when they get their first mobile phone, learn how to use computers and get their hands on video games. Screens in some shape or form are now a part of everyday life.
"Whilst technology brings with it many benefits, the health implications of being 'slaves to the screen' are a real concern. A sedentary lifestyle increases the risk of becoming overweight with increased risk of heart disease, high blood pressure and diabetes.
"We wouldn't deny children the right to have fun but as with anything, it's important to get the balance right - with exercise playing a major part in keeping children fit and healthy."