Large numbers of children in Britain are missing out on the natural world, a study from the RSPB suggests.
The three-year project found that only 21% of children aged 8-12 were "connected to nature".
Girls were much more likely than boys to be exposed to the great outdoors, while children in Wales had the lowest score across the UK.
The RSPB says that a perception among some adults that nature is dangerous or dirty could be holding children back.
There has been an increasing amount of research in recent years underlining the lack of contact and experience with nature among modern children.
Some have argued that this is having a negative impact on their health, education and behaviour.
In 2012, the National Trust published a report on the phenomenon of "nature deficit disorder", though it is not recognised as a medical condition.
The RSPB says its new study is the first to quantify the scale of British children's exposure, or lack of it, to the natural world.
They came up with a definition of what "connected to nature" actually means and then developed a questionnaire with 16 statements designed to assess the level of connection among children.
Some 1,200 children from across the UK were asked to agree or disagree with these statements. Only 21% of children in the UK had a level of connection with wildlife and the natural world that the RSPB believes should be realistic and achievable for all youngsters.
This "realistic and achievable" value is based on the average scores of children visiting RSPB sites or who are junior members of the organisation.
One interesting finding was the gender difference. While 27% of girls were at or above the "realistic and achievable" target, only 16% of boys were at the same level.
"We need to understand these differences," Sue Armstrong-Brown, head of conservation at the charity, told BBC News.
"Whether boys and girls are scoring differently on different questions, are girls more empathetic to nature than boys for instance? We need to analyse the data to find that out."
The report also highlighted significant regional differences. Only 13% of children in Wales achieved the basic level of exposure, compared with almost twice this number in Northern Ireland and Scotland.
Urban beats rural
The average score for London was higher than the rest of England. Overall urban children had a slightly higher connection than those living in rural areas.
According to Sue Armstrong-Brown, the attitudes of adults may be having a significant effect on children.
"There is definitely an attitude out there, in some cases, that nature is not perceived as interesting or engaging. In some cases it is perceived as a dirty or unsafe thing, and that's an attitude that won't help a young person climb a tree."
The RSPB hopes that its study will be taken up by government as one of the indicators on the state of children's wellbeing.
Sue Armstrong-Brown believes that improving the natural connection for children is not only good for the youngsters, it is crucial for the future of nature conservation in this country.
"If we can grow a generation of children that have a connection to nature and do feel a sense of oneness with it, we then have the force for the future that can save nature and stop us living in a world where nature is declining," she said.
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