A quarter of children spend less than half an hour outdoors each day, the National Trust has found.
More than half of youngsters aged seven to 12 spend less than an hour a day outside, while almost nine in 10 children have never taken part in traditional outdoor activities such as playing conkers or building a raft, according to research by the charity.
The National Trust said it had launched a campaign to "connect the cotton wool generation with nature" by getting 200,000 children playing outside this summer.
According to a poll of 1,000 parents and grandparents, 54% of children spend less than an hour outside each day, while one in four (25%) seven to 12-year-olds are outdoors for less than 30 minutes a day.
This compares to parents who spent an average of two hours and 34 minutes outside each day in their youth, the survey found.
More than half of grandparents (53%) spent more than three hours a day playing outside when they were aged seven to 12, compared to 6% of children today.