"There is only one substance that the modern child is allowed to handle quite freely," educator Dr. Maria Montessori wrote in The Absorbent Mind, "and that is sand."

Perhaps that's why the gritty material is a Finalist for the National Museum of Play's 2021 National Toy Hall of Fame.

"Sand may be the most universal and oldest toy in the world….

"Children recognize sand as a creative material suitable for pouring, scooping, sieving, raking, and measuring. Wet sand is even better, ready for kids to construct, shape, and sculpt. Sand provides unique opportunities for tactical, physical, cooperative, creative, and independent free play."

Even better, the stuff is literally dirt-cheap. Sand—real sand, not that Kinetic Sand stuff—is like three bucks and change for a 40-pound bag, and some of you live in places where you can get it for free, if you can carry a bucket.

World's oldest playground? (Image: Luca Galuzzi, CC BY-SA 2.5)