Best-selling author Michael Morpurgo has warned that children are becoming more isolated because of overuse of social media.
The former Children's Laureate and War Horse writer is raising money for his charity, which puts young people on farms to "milk, dig potatoes and help with hay-making".
Morpurgo, 73, said that children's "experience of life" was often limited to technology, whether it is "phones or iPads".
"The misuse of this technology is allowing this to become such a strong culture of communication that children forget about talking to people," he told the Press Association.
"They get on social media just like that, in their bedrooms, and that can be very isolating."
Morpurgo, who is best known for his children's novels, many of which have been adapted into films, said that "used properly" new technology can have extraordinary benefits.
But he warned: "A lot of children are suffering from too much isolation. Incidences of depression and mental illness are increasing.
"We live in a world which should be much happier. We have creature comforts, we're not freezing cold, we have a health service that's enabled us to have another 10 years of life... but we have more isolated lives.
"Isolation is the main culprit when it comes to mental illness and it is not helped by social media."
His warning comes after Childline reported that more children are growing up feeling lonely.
The award-winning author, who admitted that he too spends "far too much time on an iPad when I should be talking to people", said that parents should limit children's time on mobile phones and tablet computers.
"There should be very careful and restricted use until a child has developed some sense of what they are to be used for," he said.
"Up until 11,12 or 13, it should be limited - you don't have it on for more than an hour a day - parents should keep an eye and mobile phones should not be allowed in school.
"There are certain areas of life, like family and school, where you communicate by words, by talking to people. It is a life skill."
The former primary school teacher added: "We know a vast amount of bullying goes on and writing personal remarks on social media is much more insidious than fights in the playground."
Morpurgo is holding an event on May 3 at the Royal Geographical Society in London to raise money for his charity Farms For City Children, where young people "put on their wellies and coats and become farmers for a week".
Guest speakers, talking about nature and education, include actress Juliet Stevenson, broadcaster Ian Hislop and poet Roger McGough.
"When the kids come to the farm they don't have phones and they really do not die! It means they can focus on the people around them and what they're doing," Morpurgo said.
An "all-round education" is "what fires children up, not sitting in the classroom and just doing punctuation".
"That's part of it but it's not what's going to fire up their boilers to get on with life," he said.
Morpurgo, who has had around 100,000 children visit three farms in Devon, Wales and Gloucestershire over the last 40 years, said: "These are real farms not play farms.
"The children get involved with the milking, they lamb, dig potatoes, help with hay making, they do everything that's useful to the farmer.
"They really get to know where their food comes from and about the countryside, which is theirs as much as anyone else's
"They come from a place where they look out of the window and you see tarmac, concrete, planes flying overhead and the air doesn't smell very good sometimes.
"You suddenly find yourself in another world with the fields and the rivers, you see buzzards flying, herons on the rivers, the blossoms on the trees. They have this extraordinary experience of life which you never forget.
"A lot feel disenchanted already and we put a fork in their hand and give them a job to do where they can see the results.
"Every child in the country should have experience of this kind... Over the years we've received no help or support from the government at all."
Morpurgo's books include Private Peaceful, Friend Or Foe and Why The Whales Came, while the stage adaptation of War Horse premiered at the National Theatre in 2007 and went on to tour the world.