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.
Stick foam numbers (or simply write) onto plastic garden label sticks. Hide the sticks in the garden and then send the kids outdoors to find them. Once found, ask them to line up the sticks in the correct order.