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.
ضعه في وعاء محكم.