In the Bernard van Leer Foundation's Working Paper #57, Children's Right to Play, Stuart Lester and Wendy Russell from England examine the importance of play...

"The importance of play lies with developing physical and emotional flexibility, by rehearsing the actions and emotional aspects of being surprised, temporarily disoriented, or unbalanced.  Children modulate novel behaviour patterns and emotions by the frame in which play occurs and by the lack of serious consequences from losing control.  Such uncertain experiences develop behavioural improvisation that draws on conventional movements alongside atypical and novel responses, accompanied by widening repertoires for avoiding emotional over-reaction and harmless stress.  Play operates as a calibrating or mediating mechanism for emotions, motor systems, stress respon se, and attachment systems. 

"The features that distinguish play from other behaviours may exist to keep the brain labile; that is, to maintain its potential for plasticity and openness rather than close down potentiality through rigid and stereotypical behaviour patterns.  The ability to create a virtual reality offers the chance for excitement and enjoyment through temporary suspension of the limits of the real world.  This in itself becomes a self-reinforcing process, one in which motivation and reward work in a continuous cycle to support emotional and bodily engagement with the social and physical environment.  As Brian Sutton-Smith comments, play prepares you for more play, and more play offers a greater satisfaction in being alive." (reprinted from Childcare Information Exchange)