The dangers of traffic was one of the main deterrents to playing outside

A survey - Play Space - of 800 children aged between four and 16 found nearly two-thirds (61%) found things to prevent them enjoying playtime outside.

The questionnaire - to mark national playday - found 25% felt unable to play outside for fear of being bullied by older children and 17% were deterred by the dangers of traffic.

Parents' fears of strangers approaching their offspring prevented 15% of those questioned from playing outdoors.

But children's fear of strangers prevented just 6% amusing themselves outside.

Play reform

Dirty play areas, such as those fouled by dogs, were of concern to 10% and drug dealers were cited by 8% as a deterrent to playing outside.

Where children play out most often (unprompted)

Street 27% Garden 27% Park 22% Playground 9% Fields/wood 5% River/lake 3% Shopping centre 3% Home 2% Friend's house 1% School 1% Source: Play Space survey

The two charities want more funding to create and improve play spaces and more park wardens to ensure parks are safe and clean.

They are also calling on local authorities to create safer routes to parks and playgrounds and to consult children when designing new play spaces.

Ian Sparks, chief executive of the Children's Society, said there was a serious message behind national playday.

"Play is vital for children's development - it's the way children develop social understanding, explore their creativity and learn about the world around them," he said.

'Couch prisoners'

But cars, bullying and parents' fears about strangers were turning them not so much into couch potatoes as couch prisoners, he said.

The impact of not playing outside on the health and well-being of children could be "disastrous" Mr Sparks added.

It is feared children are being "crowded out" of their neighbourhoods

Tim Gill, director of the Children's Play Council, said: "Too many playgrounds and parks are dangerous, run down or just plain boring.

"We need to reclaim our parks and communities and make sure they are safe places where all children can play," he said.

Secretary of State for Culture, Media and Sport, Tessa Jowell, said: "Play is at the heart of a happy childhood experience and it is only right that there should be a day on which we celebrate this important area of children's lives.

"I believe that it is particularly important to offer children play spaces which, while being challenging and exciting, are safe, accessible and close enough to where children live to be part of their familiar landscape from an early age."