Play is an essential part of children's development and should not be neglected, says Play England.
A spokesperson for the project said: "Play is essential for a good childhood - for all children's development and well-being.
As adults, we need to make time and space for children to play freely, she added.
Previous research by Play England suggests that over 70 per cent of adults said they played outside every day. Today the figure is 21 per cent.
The news follows a survey by the National Trust which found that almost four in five children say that they would like to spend more time outdoors and less time watching TV or playing computer games.
Almost a quarter of young people spend more than 14 hours a week sat in front of the TV or a computer screen.