After your child has gotten his or her fill (and you have, too, of course), transport the moon sand into an air-tight, resealable container. Keep it in a cool, dry location, like in a closet, under the bed, or in a toy box. When you go to play with it again (it keeps a few months, though it's cheap enough you could always make a new batch), bring it back to life with a few tablespoons of water. Start molding the sand with your hands to work the water in, and it'll be good as new in no time.
ضعه في وعاء محكم.