Swings. I feel like they are the outdoor equivalent to a block as far as timeless stimulating play objects go. While the body is engaged in gross motor coordination, balance, muscle development, and sensory integration, the mind is making believe situations and stories. The swing was a costume that allowed the kids to be seahorses. It was a catapult for them to be bombs and “asplode” on. They were airplanes, and they were flying. They figured out every possible combination of piling up to fit all three of them on the same swing. They figured out how to make another swing in the yard so that there were enough swings for all of them. There were no arguments or conflicts, just organized negotiations and tons of laughter. Cooperative play at its finest.