By age 3, preschoolers have developed the large motor skills to control and direct many of their movements. Many are now comfortable walking up and down stairs without support, jumping, and walking backward.
References
Shelov, S. P. (Editor-in-Chief). (2004.) Caring for Your Baby and Young Child: Birth to Age 5. The American Association of Pediatrics. Revised edition. New York: Bantam Books.