I remember reading something somewhere about the real issue with risk and playgrounds... that modern playgrounds often hide risk, whereas older playgrounds it would be more obvious. The idea is that there were clearly places (high up, requiring climbing skill) in the old playgrounds that kids would slowly work their way up to conquering. Because the risk was obvious, kids would approach it with caution and build up skills to get there. In contrast, a lot of injuries occur when 'safe' playgrounds have kids try to do things not designed for, but because of the way they are made don't appear to be dangerous bus actually are. Giving kids the ability to assess risk accurately, and develop the skill to take that risk, is the important part.