An excellent article in today's Guardian Education section outlines how research findings are accumulating in support of the children learning through play well into key stage 2, "up to around 8." Five types of play are identified: physical, symbolic, with rules, with objects, and pretence. A variety of skills are developed through each. Click here to read the article.
Incidentally, the definition (quoting Lego's Education Head Hanne Rasmussen) of play as "a playful state of mind in which...you are open and try different things and are in a positive flow" also describes a state of being I rediscovered, as an adult, through the Alexander Technique.