The two sofas were upturned in the bay window, the coffee table was on its side, stuff was strewn everywhere round the living room - cushions, blankets, even hacked-up bits of Christmas tree. Burglars? A crudely written message was Blu-Tacked to the wall: "No adults!" Ah, just the kids, den-making.
Even though my two children are aged six and 10, up until a few weeks ago they hadn't ever made a single den. In fact, I hadn't really thought much about dens since my own den-rich childhood. That is, until BBC Radio 4 asked me to research them for their programme, Questions, Questions.
Yet, once Louis, Ynys and their friend Pelumi had free rein of the living room, and were told they had to create a den so that I could record the process, they went at it with a vengeance. The sheer gusto with which they dismantled and reassembled the living room in a way that excluded adults made me feel bad that they hadn't been doing it every day.
But we are not alone. New research by academics in the US and Scandinavia is showing both that dens are crucial to children's development - and that the opportunities for and inclination of children to make them are in danger of disappearing completely.
When Roger Hart, New York's City University's environmental psychologist, researched dens in Vermont in the 70s, he found that 86 children, aged three to 12 years in one town, had made at least one den. His follow-up research is showing that, today, hardly any of the children in that same town have dens at all and, those who do, have pre-manufactured ones. One child, when asked to name his "secret place", called to his mother for help in identifying such a spot.
Hart believes a variety of factors are affecting children's lives out of doors. Families are generally smaller in number and often both parents work, so scarcer time together means that fewer children get less attention, and when they get it, the parents tend to feel more anxious about their children's welfare. Outdoor spaces are also becoming increasingly limited in what they offer because of fear of litigation, and the increased availability of electronic media lures children indoors. But, perhaps, above all, there is parents' fear of letting children out alone.
The book critic Dinah Hall has noted a near-total absence of dens in contemporary children's literature. "Parents are too paranoid about letting children out of their sight to even be able to bear a den in a work of children's fiction," she says. "The most you're going to get is a lovely, but very tame den, under a table in a Shirley Hughes picture book."
In Norway, the situation has been judged so grave that the government has actually been paying children to make dens for the past decade through a project called "Try Yourself" - yes, paying children to do something that one might think should be an automatic, unquestioned part of childhood. Anne Trine Kjorholt, a child-researcher at the University of Trondheim, has argued that the Norwegian government's project reflects "children as an endangered people".
An endangered people, just because they can't wreck a bit of their environment? Dens are piecemeal, scrappy-looking and rarely that permanent. Why, exactly, are they so important?
Almost everyone you talk to over the age of about 25 has memories of den-making that make their eyes light up. A round-robin email between friends, wondering if anyone had any den-related memories, elicited a surprising number of responses. Alastair recalls using rubber-band guns to keep his sisters out of his dens, and holding the cat hostage when necessary. The den in Sarah's bedroom was constructed so that she and her friend could, using knives, skewers and screwdrivers, dig through the wall and spy on the au pair on the toilet.
"The den is the child's sense of self being born," says David Sobel, a developmental psychologist at Antioch New England graduate school. He has researched dens extensively since the 70s, in Devon, England, and the Caribbean. "In the middle childhood, ages seven to 11, a den is the child's chance to create a home away from home that is secret, and becomes a manifestation of who they are. The den," Sobel argues, "is the chrysalis out of which the butterfly is born."
One correspondent, who prefers to remain anonymous, says that his developing sense of self was very bound up with dens. "I was a constant den-maker," he remembers. "In fact, my entire youth, from the age of about four to 14, was spent constructing them, initially with dressing gowns and curtains. Then, later, mud pits were a speciality. Once we dug a hole about four feet deep and covered it with branches, leaves and moss, and monitored traffic on the nearby road, SAS style. All well and good until a sheep fell in and had to be rescued by a farmer. And later, that same day, we were given a roasting by the driver of a Citroen 2CV for throwing eggs at the car (clearly, we were not that well hidden)."
Already, this is enough to make many parents shudder, if only because of the thought of the amount of washing that must have been necessary afterwards. Maria Kylin, of the Swedish University of Agricultural Sciences, has researched dens from the urban planner's perspective. She believes they are critical because, "They allow children to experience danger in a secure environment. They are places in which children can challenge themselves, mentally and physically, in preparation for the rigours of adulthood."
Sobel recalls a pivotal den experience of his own childhood: "There was an older boy in my neighbourhood whose fort was a completely mysterious and alluring place for me." Yet, when the young Sobel did, finally, thrillingly gain access, it became clear that, "I was the day's entertainment." He was required to leave his trousers in the den and walk home humiliated. He concludes soberly, "The fort was the world with its own rules, away from adults."
During her research, Kjorholt also found that dens are about learning to be adults. In many of the cases in Norway, she discovered that the help of adults was actively solicited, particularly by boys over the age of about 10, whose dens, out in the forest, tended to become sophisticated huts. Grandfathers were asked to help saw wood, fathers were asked for advice on appropriate insulation material for wall cavities. And both father and grandfather were then enlisted to help transport materials in wheelbarrows. The boys wanted the men involved, because they were learning how to be men.
And Maria Kylin believes it's not just possible, but essential, to start incorporating the principles of den-making in urban planning. Her research, as a landscape architect, of children aged nine to 13 in a small town in Sweden, has convinced her that children and adults perceive their physical environment in ways that are fundamentally at odds.
"Adults have a visual aesthetic. They want a space to be functional, beautiful and, generally, clean, that to a child's eye is barren. Kids don't experience a space primarily through visuals. They are interested in what they can do in it. They like bushes. They like hidden corners. As urban planners, for example, we can look at the walk to school, we can look at open spaces in housing blocks and try to make them not only secure, but also challenging."
Sobel, following a successful pilot scheme with Steiner schools, is fighting to get den-building included in the curriculum. He reports that teachers find the dens the children have built themselves prove particularly conducive to meditative activities, such as writing journals. The toy company Mattel has been so struck by the potential of dens to improve creative thinking, that in their US head office they've installed one, complete with a life-sized tree trunk - a place where its (adult) employees are sent to brainstorm.
But what can be done for our own children, now?
For a start, don't book up a hotel or cottage for the summer holidays. Dust off your tent and take them camping. Then let them slip off to the hedgerows with their peers, to make mischief. If you live in the country or have a large garden, great. Send your kids off this minute, with hammers and nails and a picnic, and instructions to not come back until teatime.
Or, get the bits and pieces of cushions and old covers and broom handles that Sobel would call the essential "loose parts". Cook up some really nasty feast that will serve, once the den is finished, to "consecrate" the space (I used to flavour raw jelly cubes; prawn cocktail crisps dipped in hot chocolate can also go down well.) Then, get the vacuum cleaner ready, snap on your rubber gloves, and - give the kids the living room.
Making a forest den
Select a site
· The "forest" could be in a back garden or local park, but woodland provides more excitement
· Make sure there is plenty of dead wood in the area to use as building materials
· Find a feature that could be used as a starting point, such as a large log or a leaning branch
· Avoid hollows, which will become waterlogged, or dense canopies of leaves, which will continue to drip for a long time after rain
Construct the den
· Collect three long branches to form the basic structure. Bind them together at the apex with string or stems such as blackberry runners, honeysuckle or wild clematis
· Secure additional branches along one side to make a framework, again binding them in place with natural materials
· Weave smaller twigs and stems through the framework to create a lattice. This must be able to provide a firm mesh suitable for supporting a thatch of leaf litter and grass
· Lay leaves and grasses over the lattice at ground level and working upwards
· The finer details will depend on the children, they may wish, for example, to sweep the floor to clear a smooth place to sit with their friends, or to build up layers of leaf litter to create a soft bed
· This is an extract from Nature's Playground by Fiona Danks and Jo Schofield (Frances Lincoln)
· Questions, Questions is broadcast on Radio 4 at 3pm on Thursday April 20