Ginny Varga of the Center for Montessori Teacher Education explains the sensitive period for movement for infants and toddlers.

Montessori recognized early on that infants and toddlers develop knowledge rapidly in the areas of movement, order and language.
Early drafts of the next two podcasts on the sensitive periods of movement and order are now available on YouTube to review.
Movement: http://www.youtube.com/watch?v=I2qhq3GwyWQ
Order: http://www.youtube.com/watch?v=AE6NpPI0zs4