After observing children on playgrounds in Norway, England and Australia, Dr. Sandseter identified six categories of risky play: exploring heights, experiencing high speed, handling dangerous tools, being near dangerous elements (like water or fire), rough-and-tumble play (like wrestling), and wandering alone away from adult supervision. The most common is climbing heights.

“Climbing equipment needs to be high enough, or else it will be too boring in the long run,” Dr. Sandseter said. “Children approach thrills and risks in a progressive manner, and very few children would try to climb to the highest point for the first time they climb. The best thing is to let children encounter these challenges from an early age, and they will then progressively learn to master them through their play over the years.”

Sometimes, of course, their mastery fails, and falls are the common form of playground injury. But these rarely cause permanent damage, either physically or emotionally. While some psychologists — and many parents — have worried that a child who suffered a bad fall would develop a fear of heights, studies have shown the opposite pattern: A child who’s hurt in a fall before the age of 9 is less likely as a teenager to have a fear of heights. –via Can a Playground Be Too Safe? – NYTimes.com.