Children are being pushed out of public places because of excessive traffic and adults' fear of anti-social behaviour, says a report from a play charity.
Traffic dominates cities and children are unable to play, says report
There are now three times more cars than children in the UK says a report commissioned by Play England.
The disappearance of places where children can play demands a "robust and urgent response", says the report.
The report calls for a hotline to identify anti-social adults who obstruct children from playing outside.
"With cars outnumbering children by three to one, the acceleration of house building, and the privatisation of public space, places once used by young people for playing and exploring rites of childhood are quickly being swallowed up," says the report's co-author, Celia Hannon.
There are 33 million cars in the UK, says the report, compared to a population of 11 million dependent children.
The report, produced for Play England by think-tank Demos, proposes that more cities should adopt 20 miles per hour limits in residential streets where children might be playing.
And it highlights community projects which have temporarily closed roads to cars.
But the report presents a picture in which too few children walk to school and too many are shuttled in cars between their front door, school, shops and organised activities.
Unable to play outside, young people explore life through the screen of their computer games or DVDs, suggests the report.
Children are being "segregated" from public places and they have few places to play which do not lead to friction with adults.
Unless children are shopping or in structured activities, they are assumed to be "causing trouble".
Streets and parks need to be accessible to young people, says the report. It also calls for an "anti-social behaviour hotline" for children to report adults trying to stop "their legitimate right to be and play outside".
Adrian Voce, Play England's director, said the report "addresses one of the most serious challenges we face as a society: the disappearance of children and young people from public space".
"The consequence is a decline in their opportunities for play, recreation and their own social and cultural lives other than through electronic media or highly structured activities."