It is a scene that epitomises childhood: young siblings racing towards a heavy oak tree, hauling themselves on to the lower branches and scrambling up as high as they can get. Yet millions of children are being deprived of such pleasure because their parents are nervous about exposing them to any risks, new research has revealed.

A major study by Play England, part of the National Children's Bureau, found that half of all children have been stopped from climbing trees, 21 per cent have been banned from playing conkers and 17 per cent have been told they cannot take part in games of tag or chase. Some parents are going to such extreme lengths to protect their children from danger that they have even said no to hide-and-seek.

'Children are not being allowed many of the freedoms that were taken for granted when we were children,' said Adrian Voce, director of Play England. 'They are not enjoying the opportunities to play outside that most people would have thought of as normal when they were growing up.'

Voce argued that it was becoming a 'social norm' for younger children to be allowed out only when accompanied by an adult. 'Logistically that is very difficult for parents to manage because of the time pressures on normal family life,' he said. 'If you don't want your children to play out alone and you have not got the time to take them out then they will spend more time on the computer.'

Voce pointed out how irrational some of these decisions were. Last year, almost three times as many children were admitted to hospital after falling out of bed as those who had fallen from a tree.

The tendency to wrap children in cotton wool has transformed how they experience childhood. According to the research, 70 per cent of adults had their biggest childhood adventures in outdoor spaces among trees, rivers and woods, compared with only 29 per cent of children today. The majority of young people questioned said that their biggest adventures took place in playgrounds.

Voce said Play England was determined to spread the message that children ought to be taking risks and that it is 'not the end of the world if a child has an accident'. The latest study will be launched on Wednesday to coincide with Play Day, when hundreds of events will take place across the country to celebrate children's right to play. It will show that play providers also feel the opportunities for children to 'test and challenge themselves in play involving a level of risk' have reduced over the past decade. They blame overcautious health and safety officers and the fear of litigation if children have accidents.

Andrea Quaintmere, who manages Toffee Park Adventure Playground in London, admitted there were fears that parents would sue if children were injured. But she said that should not stop workers ensuring children experienced lots of adventure. 'We need to educate parents who are worried about their kids having accidents and hurting themselves,' said Quaintmere. 'Children can learn from small accidents. Parents do get nervous and tell us "don't let them do that". I try to remind them of their own childhood.'

As Quaintmere spoke, two nine-year-old girls, Chloe Bailey and Kiara Gomes, ran by. 'My favourite games are football and "it",' said Chloe, before going to build a camp with her friends. 'My mum says that climbing trees is too dangerous,' said Kiara. 'But my dad lets me. If I fall over and it hurts, I just get myself up and smile.'

The Play England study quotes a number of play providers who highlight the benefits to children of taking risks. 'Risk-taking increases the resilience of children,' said one. 'It helps them make judgments,' said another. Some of those interviewed blamed the 'cotton wool' culture for the fact that today's children were playing it too safe, while others pointed to a lack of equipment or too much concrete in place of grass. The research also lists examples of risky play that should be encouraged including fire-building, den-making, watersports, paintballing, boxing and climbing trees.

Justine Roberts, founder of Mumsnet.com, an online forum for mothers, said that parents only wanted to protect their children. 'It is the mums and dads that have to deal with the bruises and cuts,' she said. 'But broadly speaking I think that we will have to be brave and allow our children to take physical risk because, within reason, that is the way that they learn.

'When you see your two-and-a-half year-old on a climbing frame your heart is in your mouth and that is normal but I think most parents realise that at some point their children have to take physical risks; most recognise the benefits of learning through play. We can be overprotective but it is impossible to wrap children in cotton wool.'