Kids as young as two should not be allowed to watch too much TV, for it can do more harm than good to their ongoing development, according to a leading child expert.
Professor Dimitri A Christakis, from the Seattle Children's Research Institute and the University of Washington, USA, has also expressed considerable concerns about DVDs aimed at infants that claim to be beneficial.
In a 25-year review of 78 studies, Christakis found that nine in ten children under the age of two watch TV regularly, despite ongoing warnings, and some spend as much as 40 per cent of their waking hours in front of a TV.
In a 2007 survey conducted over 1,000 families, parents said that they let their infants watch TV because they thought it was "good for their brains".
But watching TV programmes or DVDs aimed at infants can actually delay language development.
A Thai study had shown if children under 12 months watched TV for more than two hours a day they were six times more likely to have delayed language skills.
Another study found that children who watched baby DVDs between seven and 16 months knew fewer words than children who did not.
In another study, the researchers looked at the effects of early TV viewing on cognitive development at school age and found that children who had watched a lot of TV in their early years did not perform as well when they underwent tests to check their reading and memory skills.
On possible explanation, according to Professor Christakis, is the fact that it exposes children to flashing lights, scene changes, quick edits and auditory cuts which may be over stimulating to developing brain."
"TV also replaces other more important and appropriate activities like playing or interacting with parents," he added.
The review is published in the January issue of Acta Paediatrica.