This summer I read---and reread---a monograph entitled: Children's right to play. It was written by Stuart Lester and Wendy Russell for the Bernard van Leer Foundation in December 2010. Their starting point is Article 31 of the United Nations Convention on the Right of the Child. In that article, they specifically cite the right of the child to engage in play. For them it is a necessity of life for children. It is not a vehicle adults use to teach children about the world, nor is it a way to make academics palatable to children. It is an activity undertaken for its own sake that is wholly owned by the children.
They go so far as to cite research that children need to engage in play for their very survival and well-being. They say: "Children's play can be seen as a self-protecting process that offers the possibilities to enhance adaptive capabilities and resilience. ... Play acts across several adaptive systems to contribute to health, well-being and resilience. These include: pleasure and enjoyment; emotion regulation; stress response systems; attachments; and learning and creativity."
At one point in the paper, they reference a comment by Brian Sutton-Smith. The comment states: "Play prepares you for more play, and more play offers a greater satisfaction in being alive."
Take a look at the following pictures from the sensory table to see if the children exude that "greater satisfaction in being alive."