Just a quick continuation on the topic of free-play...
Richard Louv discusses in Last Child in the Woods how the rise of living as secondary experience where everything is filtered through visual and audio technology is creating a situation where children essentially do not learn anything of genuine substance.
Here he quotes Robin Moore of North Carolina State University:
Children live through their senses. Sensory experiences link the child's exterior world with their interior, hidden, affective world. Since the natural world is the principle source of sensory stimulation, freedom to explore and play with the outdoor environment through the senses in their own space and time is essential for healthy development of an interior life. This type of self-activated autonomous interaction is what we call free-play. Individual children test themselves by interacting with their environment, activating their potential and reconstructing human culture. The content of the environment is a critical factor in this process. A rich open environment will continuously present alternative choices for creative engagement.
Another voice with a fresh perspective on why free-play is a critical component of curriculum!