Mud pie kitchen for kids. Great idea for some messy and fun outdoor play. If you don't want mess of mud you could use Play Sand: In a large, plastic storage container with a lid, mix together 9 cups of clean play sand with 3 cups of cornstarch. Add 2 1/2 cups of water, stir, and start building. Close the lid when the sands not in use. Just add a bit of water if it dries out.