Two Norwegian psychologists think that modern playgrounds are for wimps. Instead of short climbing walls, there should be towering monkey bars. Instead of plastic crawl tubes, there should be tall, steep slides. And balance beams. And rope swings. The rationale is that the more we shield children from potential scrapes and sprained ankles, the more unprepared they’ll be for real risk as adults, and the less aware they’ll be of their surroundings. Leif Kennair and Ellen Sandseter’s ideas have won the support of playground experts on both sides of the Atlantic; one company, Landscape Structures, offers a 10-foot-high climbing wall that twists like a Möbius strip.