They're cheap or free. They engage a child's creativity and encourage peer play and social cohesion. Loose parts playgrounds are popping up in many parts of the world.
The good news is that you can create one in your own backyard. Or even just add some loose parts to an existing playground.
Loose parts are excellent at drawing out a child's imagination as they inspire children to practice creative thinking in sorting out how to incorporate the part into play. You can gather an assortment of manmade objects such as bedsheets, canvas, pulleys, rope, buckets, milk crates, pots and pans. And natural objects like pebbles, seeds, sticks, stones, water. Then just sit back and watch the ideas flow: Pebbles + cardboard tubes = a marble run or rain stick; Branches + fabric= a little house for little people or animals.
The Australian group, Playground Ideas, has created a DIY guide for creating your loose parts playground. The excellent guide includes a wide range of tips from assessing your site for safety to budgeting for and obtaining your loose parts.