Why Play in Sand?
There is no right way to use sand. It invites participation; it permits children to make and test hypotheses; it stretches the imagination; it provides a potentially soothing sensory experience; and it is an excellent avenue for children to learn physical, cognitive, and social skills.
Because sand play is open-ended, the child determines the direction and path of his or her own play. This freedom then clears the way for the child to build developmental concepts.
According to constructivist theory (Piaget, 1945), children have an inner drive to build an understanding of their world as they explore and interact with materials. Concepts about how the world works are built gradually and become increasingly complex as the child enters a rich learning environment and exercises his or her freedom to play.
Click here for source