Parents let children use the internet aged three with many spending two hours a day online before they start going to school Many children spend four hours or more on smartphones and computers The average age parents let their children start using the internet is three One in 20 children admit they arranged to meet someone they met online Parents typically let their children start using the internet aged three, a survey reveals. And it quickly becomes a habit. By the time they are at school, children spend an average of two hours a day online - twice as long as their parents realise. Nearly a third of parents fail to put any restrictions on web use. Early start: The average age parents allow their children to start using the internet has crept down to three The report shows how youngsters are putting themselves in danger through risky activity, losing traditional moral boundaries, developing mental health issues and even suffering physical problems from the hours they spend slumped in front of screens. Yet the average age parents now allow children to start using the internet is three. Many then go on to spend four hours or more every day on computers, tablets and smart phones. One in 20 children admitted arranging a secret meeting with someone they met online, according to the Netmums poll. Well over half have accidentally stumbled on "inappropriate" content including porn, eating disorder sites and self-harm images - although one in nine admitted looking for it deliberately. Screen time: Many young children now spend four hours or more on tablets, smartphones and computers every day This includes a quarter have visited eating disorder sites, one in five who have seen self-harm images and a similar proportion who watched soft porn. One in 16 have been exposed to hardcore pornography. A fifth have "thought about trying" what they saw. One in 16 ended up restricting their eating and one in 30 had self-harmed or considered or tried suicide. Just over one in 100 acted out sex scenes they had witnessed. One in 12 have exchanged messages with sexual content to other people, while one in 25 have sent graphic photos of themselves. The Daily Mail has campaigned for an automatic block on online porn, with access to adult sites only possible by opting in following an age check. A third of children admitted they spend so much time on the internet they struggle to concentrate on other activities, such as reading a book. One in nine have put on weight because of the hours they spend surfing the internet or using social networking sites. And a fifth admit living in the virtual world more than they do with real people. Many showed tell-tall signs of addiction, with a third feeling "angry or grumpy" if they can't get online. Last week it emerged a four-year-old girl was being treated for iPad addiction. One in 12 parents have noticed their children's concentration has suffered with offline activities and one in 50 spotted a decline in conversation skills. Yet many fail to realise there are problems and those that do spot warning signs often fail to take action. One in seven parents are allowing their children remain online for four hours or more every day. And over a quarter of children get away with pretending to be older to get an account online such as Facebook, which is meant to limit services to 13 and over. Three-quarters of parents have used a ban on screen time as the modern equivalent of "grounding kids" - although one in eight children get around this by using it behind the adults" backs. The survey of 825 children aged between seven and 16 and 1,127 adults found one in eight parents allow their child to use the internet from the age of two. Just one in ten make their child wait until they are ten or older. Netmums co-founder Siobhan Freegard said: "No past generation has ever had so much access to so much information so fast - and not all of it desirable - along with the use of dozens of different electronic gadgets. Some scientists have predicted large amounts of internet exposure may alter the way kids think and in many ways we are in the middle of a giant experiment with our children as the subject. We are raising a generation of technical geniuses - but at what cost?