Martin Large, author of Set Free Childhood
Children under three should not watch TV at all and should watch as little as possible up until the age of seven. From seven to 12, they should be allowed to watch suitable programmes, but with close parental supervision. They should be shielded from electronic media as much as possible - computers as well as TV.
TV is neurologically damaging - it is too fast-paced and over-stimulating and isn't at all creative; free time should be spent on play activities and story time. A study of 1,000 children in Manchester in the 1990s found that a fifth of the children observed had listening and attention problems which impeded their language development. The constant background noise of the television dulled their sense of hearing and the lack of verbal interaction with their parents meant they were unable to recognise basic words.
Dr Jeffrey Johnson, Associate professor of clinical psychology, Columbia University
The American Academy of Paediatrics recommends that parents should limit children's TV viewing time to two hours a day. Ideally, young children should not watch at all. Television is highly addictive and it is often very difficult for children to turn the set off. Parents can help by encouraging their children to have a wide range of interests - including physical exercise, interacting with other children, reading, art and music. Moderate viewing of educational programmes can help the development of language skills but even high-quality TV programming can be problematic if viewing displaces other important activities.
A child's mind is highly impressionable and the habits we establish during childhood often stay with us throughout our lifetimes. Our research indicates that adolescents who spend too much time watching TV are more likely to experience frequent sleep problems by early adulthood. We found that the risk could be reduced if teenagers restricted their viewing to less than an hour a day.
Liz Attenborough, manager of the Talk to Your Baby campaign at the National Literacy Trust
A lot of the research as to how children are affected by TV comes from America and as such is slightly misleading, in that British TV is quite different from US TV. There are lots of high-quality, carefully prepared programmes for early-years in this country. Programmes with a single gentle voice are most suitable for very young children - multiple voices are extremely confusing in the pre-school years.
It is actually more useful to watch videos of children's programmes as this fosters a certain familiarity with particular programmes and encourages anticipation and so on. No child learns a word from hearing something once and repetition is important in developing in language skills. It is also important to remember that it is OK for children to enjoy watching television - everyone needs to have some time to relax and be entertained.
The context in which TV-watching occurs is key - if you talk about a programme after watching it, children are likely to gain more from the experience.Constantly having a TV on in the background actually distracts adults and discourages them from interacting with their child which is one of the main ways that parents can help to foster and improve their children's linguistic skills and educational development.
Louise Emanuel, consultant child and adolescent psychotherapist, and head of the under-fives service at the Tavistock clinic, London
I don't think there is any formula - it's not a case of simply saying that so many hours a day is bad or whatever. There are times when TV can be useful and comforting and watching a favourite video can help a child who is in a transitional stage such as starting school.
Very small children really need a good-quality carer who is able to monitor and manage TV or whichever input they are exposed to: all external influences should be mediated. If parents discuss programmes afterwards, it helps to make a link between what is watched and their view of the world.
If a child is left in front of the TV for a long time without any adult presence, they may end up feeling quite glazed and stop taking much in; sometimes they need to be "rescued" from such a passive situation. It is important for whoever is looking after them to be aware of how they are reacting and whether or not they feel emotionally secure.
Parents assume that children's TV is OK but they need to be observant of quality and content and recognise that the story of the Three Little Pigs can be as frightening to a young child as the Blair Witch Project is to us: stories can be scary, but there is something about visual stimuli which comes straight into the room that can be particularly powerful.