Michael Kronstadt grips the rung of the rope ladder. He is careful to keep his balance as he climbs. The ladder hangs freely from a huge tree in his back yard. At the top -- 15 feet above the ground -- Michael hoists himself through a narrow vee between two thick branches so he can stand on the platform of the tree house he helped build and survey the neighborhood.

On nice days like this, when it is great to be outside, Michael, 11, and his sister Jamie, who is 9, are drawn to their tree house in their Kensington back yard. They clamber up the ladder to read, play with friends, spy on their neighbors and wage battles with super-sized water guns.

Above the fray, there is a sense of security in knowing that the tree house is a special place built just for them. But there is also a sense of danger. The windows are low and deep, without railings to protect against falls, and there is a tight, precarious space at the top of the ladder where you could lose your balance and plunge to the ground. Art Hansen, a family friend of the Kronstadts, who designed and constructed the treehouse, purposely built what he considered an acceptable level of risk in the structure to teach the kids responsibility. He and the children's mother were comfortable that Michael and Jamie would be cautious.

Michael and Jamie like the challenges that come with the height. They are able to flex their muscles. They become the masters of their own universe.

Control is important to children. They gravitate to secret places where they are out of range of the hovering eyes of grown-ups. Whether they're perched up on a ledge, knee-deep in a muddy creek or hidden under the dining room table, they like a place to call their own.

"The spaces children use are quite variable," said Alice Whiren, professor of family and child ecology at Michigan State University in East Lansing. "A cardboard box, a lilac tree, an empty lot--the type of structure is not what is important. It's the ability to have some level of control over a limited domain."

In a playhouse, tent or makeshift fort, children can make decisions about what they can do. Who comes in and who stays out. It is a microcosm of the world.

The playacting that comes with re-creating a home or a classroom--the types of environments that children are exposed to daily--lets kids practice socialization skills that are necessary for development.

"We're dealing with power and hierarchies all through life," said Whiren. And children are not very powerful in making most of the decisions that affect them. Playhouses, she said, help children "learn about how to take care of themselves, how to make decisions and how to structure their environment."

The Higher the Better

Not only are playhouses a lot of fun, but they also give children an opportunity for socialization and for solitary experience. An opportunity for sharing and for owning. Michael requested a rope ladder as the only access to his house. When he or his sister wants to be alone, they pull up the steps and bask in solitude. When they want company, the ladder stays down.

He and Jamie also help to shape their identities through this play. "Height has a lot of meaning in terms of our nonverbals and our language," Whiren said. "The person on top is the most powerful person. We use phrases like 'at the top of the class,' and 'the head of the company.' We associate being up high and being powerful with being in control."

Those who scale heights to find their special place, she said, "demonstrate their physical abilities--that they are strong and competent and can see things other people cannot see. They find it rather exhilarating to view the world from another perspective. What they're doing is a little bit risky, and they're showing they're brave enough to climb the ladder."

Parents often view the risks children face today as different than the risks 30 years ago. They sometimes are afraid to let their kids roam free in their neighborhood. They weigh the danger of sending them outside alone against the security of keeping them wired to the television set. Yet it is important for children to explore the out-of-doors through play as a way to learn about boundaries, both environmental and social, said Roger Hart, co-director of the Children's Research Environment Group and professor at the graduate school of the City University of New York.

Fran Kronstadt, Michael and Jamie's mom, thought a tree house would give them more independence. Although she keeps an eye on them when they walk to the corner to mail a letter, she trusts them atop the tree in her fenced-in back yard. "They're away but they're here," she explained. "I always know if they need me they'll yell and I'll hear them, so I don't worry about them. I know they're not going to hang out the windows or off the platform. They have to learn to trust themselves and be on their own to a certain extent."

Amy Templeton, a Washington lawyer who stays home with her two daughters, has a similar view. "I was the second of four kids, and I remember wanting to be alone," said Templeton. "I shared a room with my sister, so my bedroom was not my own. To get away, I went down a couple of lots from my house and climbed a tree. In the summertime, when the leaves were out, nobody could see me. I was perched there and I read for hours and hours. It was great because it was quiet. I was out of sight, and I could spy on what was happening below me."

Templeton wanted her children to find comfort outdoors, but her back yard presented challenges. It has a steep, rocky, uneven terrain that leads down to a creek. When Kara, 9, and Ally, 5, were younger, Templeton wasn't comfortable letting them play alone. "We didn't have a lot of flat ground for a traditional swing set." What they had at the bottom edge of their property was a small strip of land--about 15 feet by 15 feet--that ran behind the creek. There the Templetons built an 8-by-10-foot cottage that has a Dutch door, painted shutters and window boxes filled with black-eyed Susans and two small bridges to cross over to it.

Ally likes to set the table, sweep and pretend to talk on the telephone in her playhouse. Kara is drawn to the creek. "One time at the tail end of a hurricane, we got a huge rainstorm. There were old Coke bottles and a bicycle wheel in the water," said Templeton. "The kids were pulling out all these treasures and examining them.

"Kara had a tadpole hospital for a while. She put a slew of them in a fish tank and fed them. It was kind of neat. Other times, she'll pan for crayfish and newts."

Kara and Ally have grown into the yard, and Templeton feels that for urban kids, they have a unique situation. There is a sense of adventure as they explore the underbrush. One of their favorite hiding places is a willow tree. The branches form a dome overhead.

Noticing natural and seasonal changes is another benefit of encouraging children to find special places outdoors. Sometimes the tree house, cottage or tent is "a vehicle that initially gets children out and interested in their environment, and then it can serve as the vantage point to start looking around," said Norm Lownds, a professor and curator of the 4-H Children's Garden at Michigan State University.

At the 4-H Gardens, Lownds is the master of 64 "theme habitats" on two-thirds of an acre of land. Some are based on stories such as Peter Rabbit. There's also a maze, a butterfly garden and an area shaped like a cereal bowl filled with plants that are used as cereal ingredients.

Although Lownds may wield administrative power at the gardens, he loses to his 6-year-old son every time he is challenged to a footrace. "There is a 4 1/2-foot archway that leads out of one of our secret gardens. When we're in there, my son will say, 'Okay, Dad, let's run out.' He can get through that arch. As an adult, I have to bend down and it takes some additional effort. He knows that arch was made for him and not for me, and that is very empowering."

When Arthur Cohen moved his family from Connecticut to Chevy Chase, his sons didn't feel at home until he built a playhouse in the back yard. It replaced their "Skyfort," a spectacular playhouse they had left behind.

Part of the enjoyment of a playhouse is in the planning, especially for parents who may be creating something they had wanted when they were children. In designing his family's playhouses, Cohen bought books, read articles and searched the Web. He found himself drawing plans wherever he traveled--on planes, in hotel rooms, and even in a Paris cafe.

The new fort, a multilevel structure with a tower that is built into several trees, is perfect for his children Alex, 9, and Theo, 6. It is their safety zone in games of war. They have a James Bond fantasy going, and "it's us against the trees." Playing cooperatively and not fighting is a covenant the two have made in their hide-out.

"If we didn't get along, the trees would attack us," said Alex. "We own the fort together, and that's a good feeling, because we know we can trust each other."

They also use the fort as a way to clear their heads when they're sad or angry. Climbing, tiptoeing up to peer through the spy holes, playing flashlight tag and being outside "makes us feel better. We get in the mood to play and have fun, instead of being sad," said Alex.

Putting a Child in Control

Children use their private spaces to "reenact the difficult situations that arise in their day-to-day life," explained Lisa Herrick, a clinical psychologist who works with families, adolescents and children in Washington and Virginia.

"It's a basic human need to create enclosed spaces with firm boundaries around oneself, and it's a feeling that children love," Herrick said. They love to go into tunnels, surround themselves inside blankets and hide under the covers where it is dark and cozy.

Throughout childhood, they're constantly reinventing spaces to create environments they can control. How they play often corresponds with an emotional issue in their lives and "is related to their own sense of mastery and trying to figure something out," said Herrick.

"When I went back to work, my daughter was a preschooler. She would set up our playroom to look like a playhouse with a kitchen and the front door and everything else. She'd take an old briefcase of mine and she'd make me be the kid and she'd be the mommy. She'd go to the door and wave goodbye and she would want me to say, 'Don't go, Mommy.' She was working on all of the feelings that she was struggling with about parting with me every day, and she did it by creating a house-like structure. Because this house was designed by her, she felt very safe. The dramatization made her able to tolerate something that was very hard for her--which was saying goodbye to me."

Herrick remembers that she and her friends hid out under fir trees that had very thick branches. Under the bottom branches, you couldn't be seen from the outside. "We used to drag in props from the house--chairs, blankets and food," she said. "We played getting away from bad guys when we were little.

"When you get a little older, about 10 or 11, the fort serves a different purpose. At that point kids are working on how to get along in relationships. What they do is devise intricate rules among peers or siblings around the issues of inclusion and exclusion. They have secret passwords, and they're taking turns coping with unfairness and creating hierarchies for power."

They purposely don't invite their parents into these secret hide-outs, and if all things are going well, that's good. "It's a mastery issue," said Herrick. "You can't master your own challenges if a grown-up is intruding, so it is very important to keep the grown-ups out."

In the back yard of Wendie Lubic's house in the Chevy Chase section of Northwest Washington stands a flowering cherry tree that is more than 150 years old. "It's a fabulous tree, and from the moment we moved in I had always dreamed of making a tree house in it," she said. Lubic is a single parent who lives with her daughters, Rachel, 9, and Sasha, 8, and had never built anything before. Although the idea for the tree house has been in their minds since they moved in five years ago, they began construction only last year when the kids were old enough to help.

"Practically every weekend last year we went to the hardware store and came back with pieces of wood 12 or 15 feet long hanging out of my car. Rachel and Sasha helped me drag the wood around the house, hold the wood steady when I cut it, draw the angles that I cut, and piece the wood around the trunks of the tree. After we sunk the posts into the ground, I climbed up a six-foot ladder and they handed me the wood and tools so I could lay the plank. They learned the proper behavior around dangerous tools like circular saws, and they were very important in the planning process."

Lubic was careful to preserve the tree, minimizing the number of bolts she drove into it by supporting the platform on posts of wood. The experience has been "a labor of love," she said. "We were all working toward this common goal, and they knew I was trying to make it safe for them. I think they gained a sense of accomplishment. Girls can do what boys can do. We're okay, the three of us.

"My kids love taking their friends up there, and so do I. It's great being up in the trees: You see all the neighbors' yards, kids playing, trees and flowers. It's your own private perspective, you're the fly on the wall in your private hide-out."

It's a feeling that Marian Diamond still relishes. Sixty-five years ago when she was a child in California, she used to "love to get to the top of a eucalyptus tree. I have great memories of that. I would hang by my knees and yell, 'Hey, Mom, look at me.' I wanted my mom to know I could climb higher than the other little kids."

Today, Diamond, who is 72, is a professor of integrative biology at the University of California in Berkeley. She credits her early independence with helping her reach her professional potential. To be a woman and a professor of science at Berkeley took a lot of confidence, competence, initiative and curiosity, she said.

Her studies prove what she discovered on her own as a little girl. Climbing, exercising, exploring and using imagination help to develop the brain fully. That early experience, Diamond explained, still helps in every moment of daily living because it enhanced the ability to think analytically, solve problems and have fun.

CAPTION: Wendie Lubic gets help from daughters Sasha, left, and Rachel, right, as they build a tree platform outside their home in Northwest Washington.

CAPTION: Ally Templeton, left, and sister Kara climb into the loft of their playhouse.