Children are spending twice as much time in front of a TV or computer screen as in the classroom, according to a new book on how big business targets young consumers aggressively though new media.

It says that today's children are a captive audience for sophisticated and energetic marketing techniques because they spend so much of their day online or in front of the television.

On average British children spend five hours and 18 minutes watching television, playing computer games or online each day. The total of 2,000 hours a year compares with 900 hours in class and 1,270 hours with their parents.

Consumer Kids, written by Ed Mayo, head of Consumer Focus, formerly the National Consumer Council, and Agnes Nairn, an academic, is serialised in today's Times . It warns of the dangers of relentless marketing to children through websites and other media, saying that it is an intrusion into their privacy and is destroying family life.

While parents appear to be waking up to the threat of sexual predators online, they have no concept of how business grooms their children for profit, the authors say. Children are recruited through enhanced membership schemes or special offers to promote products to their friends, while their favourite websites are peppered with advertisements made to look like content. Personal information is routinely sought, often as a condition of getting access to a site.

The book also reveals startling new data on the dominance of the media on children's lives, saying that it is hard for young people to escape from big business.

On average children spend two hours, 36 minutes watching television each day, one hour and 18 minutes on the internet and one hour, 24 minutes on a games console. “The screen can no longer be classed as an electronic babysitter that keeps children occupied,” the book says. “It is a whole electronic world in which they are immersed and which is underpinned firmly and securely by a profit motive. The conventional paradigm of childhood as a stage that evolves around family and schools has had to change. It's the commercial world that dominates the time of today's children.”

Children's bedrooms have become “high-tech media bedsits” with more gadgets than an entire family would have had a generation ago.

About 90 per cent of teenagers have a television in their bedroom, as do 60 per cent of five to six-year-olds. The trend is not driven by income, with 98 per cent of teenagers from deprived backgrounds having their own TV compared with 48 per cent from more affluent families. Two thirds of five and six-years-olds watch TV before school each day and a similar proportion watch it before bedtime.

More than a third have their own laptop or PC and two thirds have a games console. One quarter have access to the internet in their bedroom. That makes it far easier for business to obtain information and give children, including young children, a heavy sales pitch under the cover of entertainment.

One piece of research found that 85 per cent of children's favourite websites collected some sort of personal information, including e-mail addresses, users' names, postcodes, dates of birth, gender and age. Most of this information is “compulsory”, meaning that the child cannot use parts of the site without handing over these details. About 15 per cent of sites demand information to take part at all. Another 35 per cent offer ringtones, wallpaper, newsletters and screensavers in exchange for information.

The researchers say that the size of the market for children's consumer goods means that companies will stop at nothing to get information. They estimate that the total market stands at about £99 billion, up 33 per cent in the past five years, £12 billion of which comes from pocket money.

Times recommends

• Students to rate lecturers online
• Students face big rise in university fees
• Queen’s English Society boss’s poor spelling