Parents need to do more to stop children spending too much time watching television or playing computer games, according to a psychologist.
Dr Aric Sigman said "screen time" needed to have a daily limit in a similar vein to salt or alcohol intake.
He called for parents to "regain control" or they were risking a "form of benign neglect".
He will speak at the Royal College of Paediatrics and Child Health's annual conference in Glasgow later.
Dr Sigman will argue that the amount of time spent in front of screens is at an all-time high - with children having access to an average of five screens in the home and often using more than one at once, such as a smartphone and the television.
This is linked to a sedentary lifestyle, Type 2 diabetes and heart disease, he will say.
He will also raise concerns that it might be changing children's brains as they develop.
Brain scans have shown differences between the brains of gamers and non-gamers . However, it is not known if playing games change the brain or if people with certain brain structures are driven to play games.
Dr Sigman told the BBC that "there are concerns that it alters the reward circuitry in the brain" which may lead to "dependence".
"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."
He continued: "It is always the principle of caution in children, except for screen time."
He is arguing that children up to the age of three should have little or no screen time. Then a maximum of an hour-and-a-half up to the age of seven, and a maximum of two hours up to the age of 18.
The shadow public health minister, Diane Abbott, has also called for parents to cut the amount of time families spend in front of the television or playing on a computer.
She said: "By 2025, nearly half of men and over a third of women will be obese, so we've got to start helping and empowering parents to do the right thing."
The Department of Health said: "Physical activity offers huge benefits - all children should be encouraged to be active."
It said under-fives should spend as little time sitting still as possible.
Meanwhile, doctors at the conference have updated the way they check that children are growing properly.
New growth charts, which are used by doctors and school nurses to compare a child's height, weight and age, have been developed to make it easier to spot obese children and those not going through puberty properly.
Dr Charlotte Wright, who was instrumental in the design, said the new charts were "simpler to use" and would give a "more accurate picture" of the health of children.