A boy tries to light dry grass under a pyramid of twigs. Eventually, it catches and he lies on his side to blow the embers into crackling life. Tonight he and his friends will dine on a thin stew made of thistles and heather leaves, cooked over the fire. They will sleep in a makeshift bivouac on a bed of ferns. This is not a scene from Swallows and Amazons. It is an increasingly popular kind of educational holiday for children. On this particular course, groups of children aged from nine upwards will be pretty much alone. They have a...