One day, your child will pay a lot of money to roll half-naked in the sand on Spring Break. Today, they can do the same thing in this sandbox, for less!
Do we really need to explain the glory of sand? No we don't. Anyone who's ever been young knows how much fun it is to push it, dig in it, let it run through your fingers, throw it at people and laugh... wait, no, don't ever do that, shame on you. But sand is fun! It's like a beach you can set up in the backyard, where you don't ever have to worry about your child doing something stupid to win a t-shirt from a DJ who works at the local radio station.
Of course, your little one is years away from the debauchery that's currently associated with the beach. Right now, a box of sand is just a nice place to play. We've even added a nice shady canopy to keep that innocently-bared skin from getting too burned.