Washington ? Linda Pelzman appreciates the beauty of the outdoor world, sometimes pulling her children into the yard to gaze at a full moon or peer into a dense fog. An educator and founder of a summer camp, she only wishes her enthusiasm was fully shared.

On a recent nature walk near her Gaithersburg, Md., home, her younger son, 6, was unimpressed, pleading, “I just want to go back to civilization.” Her older son, at 13, has made it clear he prefers PlayStation.

“Kids don’t think about going outside like they used to, and unless there is some scheduled activity, I don’t think they know what to do outdoors anymore,” Pelzman said.

Pelzman’s view is shared by a growing number of children’s advocates, environmentalists, business executives and political leaders who fear that this might be the first generation of “indoor children,” largely disconnected from nature.

Concerns about long-term consequences – affecting emotional well-being, physical health, learning abilities, environmental consciousness – have spawned a national movement to “leave no child inside.” In recent months, it has been the focus of Capitol Hill hearings, state legislative action, grass-roots projects, a U.S. Forest Service initiative to get more children into the woods and a national effort to promote a “green hour” in each day.

Today, 40 civic leaders – representing several governors, three big-city mayors, Walt Disney Co., Sesame Workshop, DuPont, the gaming industry and others – will launch a campaign to raise $20 million that will ultimately fund 20 initiatives across the country to encourage children to do what once seemed second nature: go outdoors.

“If we really want to make a difference in this area, we need a shift in the culture,” said Larry Selzer, president of the Conservation Fund, which organized the alliance of leaders.

Advocates and researchers have been aware of the downturn in outdoor activity for a long time, and it has been documented by experts such as Sandra Hofferth, a family studies professor at the University of Maryland. From 1997 to 2003, Hofferth found, there was a decline of 50 percent, from 16 to 8 percent, in the proportion of children 9 to 12 who spent time in outside activities such as hiking, walking, fishing, beach play and gardening. Organized sports were not included as an outdoor activity in the study, which was based on detailed time diaries.

Hofferth’s study also showed an increase in computer play time for all children and in time spent on television and video games for those ages 9 to 12. And it found increases in sleep time, study time and reading time.

The increased activism has been partly inspired by a best-selling book, “Last Child in the Woods,” and its author, Richard Louv.

Coining the term “nature deficit disorder,” Louv has argued that indoor kids are more prone to a range of childhood problems, including obesity, depression and attention disorders. He contends that they miss out on the spiritual, emotional and psychological benefits of exposure to the wonders of nature, including reduced stress and improved cognitive development, creativity and cooperative play.

“I’m not saying that a child who grows up without nature is going to have terrible problems,” Louv said, “but if you look at the studies that show what nature does give kids, it’s unfortunate that so many children are missing out on that.”

With this generation of children, he said, “I think were going to pay a price if we don’t turn this around.”