Interesting idea for putting a play area on asphalt, concrete or hard soil in a temporary build. The tires and rocks can be removed, and the sand and rocks swept up. Interesting idea for day cares in urban settings without access to grass or soil.
Outdoor play! drains and gutters, exploring gravity and weights, using different balls and sticks, and rocks, I think toddlers would really enjoy the noise and dropping something and seeing where it comes out.