For all who have never climbed a tree

One of the best gifts earlier generations of parents gave to their children was a simple command, delivered again and again: "Go out and play." Those four little words offered an antidote to boredom, an outlet for youthful energy, and above all a firsthand look at the wonders of flowers and bugs, pine cones and clouds. Woods and fields beckoned, and nature became an everyday part of childhood.

Today unstructured outdoor activity has largely disappeared for many American children. Tethered to TV and video games, they lead sedentary lives. As one fourth-grader in San Diego puts it, "I like to play indoors better 'cause that's where all the electrical outlets are."

Apprehensive parents, fearful of everything from "stranger danger" to traffic and crime, also keep offspring close to home. A study of three generations of 9-year-olds found that in 1990, the radius around the home where children were allowed to roam on their own had shrunk to a ninth of what it had been in 1970. For latchkey children who return from school to an empty house, there is a stern new parental command: "Don't you dare go outside."

The result is disastrous, says Richard Louv in his important and original book, "Last Child in the Woods." Children can speak knowledgeably about the environment - the disappearing rain forest and the growing ozone layer - but many have little firsthand acquaintance with the flora and fauna outside their doors. Nature has become an abstraction, the stuff of PBS specials rather than daily life. Some children have never climbed a tree, picked violets in the spring, or watched a pale green cocoon on a milkweed leaf metamorphose into a monarch butterfly.

The loss is everyone's, says Louv, a child advocate and journalist who coined the phrase "nature-deficit disorder." He argues persuasively that children's total well being is at stake. New studies suggest that direct exposure to green growing things can reduce the incidence of Attention Hyperactivity Deficit Disorder. It lessens stress and heightens children's creativity and concentration. Above all, it increases their joy in life.

Louv finds many culprits conspiring against a nature-oriented world. Eighty percent of Americans live in urban areas, which often lack park space. In suburbs, bulldozers chew up vacant lots and woodlands, replacing them with housing and asphalt. Many condominium developers refuse to let children play on the grounds.

"Countless communities have virtually outlawed unstructured outdoor nature play, often because of the threat of lawsuits, but also because of a growing obsession with order," Louv states. Simple playhouses and tree houses require building permits.

Yet Louv remains optimistic that the trend toward the "de-naturing of childhood" can be changed, or at least slowed. Doing so will require a diverse army of parents, teachers, city planners, leaders of youth nature programs, and environmentalists. Even employers can help by giving parents flexible summer work hours. That in turn could encourage families to introduce children to nature through gardening, camping, and birding.

Louv calls for a nationwide review of laws governing private land and recreation, especially those involving children. But he concedes that dealing with the legal tangle of outdoor play will present a difficult challenge.

The rewards for such efforts will be manifold. "Nature - the sublime, the harsh, and the beautiful - offers something that the street or gated community or computer game cannot," Louv states. "Nature presents the young with something so much greater than they are; it offers an environment where they can easily contemplate infinity and eternity." The book occasionally feels repetitious. But, as Louv so eloquently and urgently shows, our mothers were right when they told us, day after day, "Go out and play."

• Marilyn Gardner is a staff writer covering family issues.