Four-year-olds have the coordination and balance of adults and can stand on one foot for ten seconds or longer. They hop, climb, and swing easily and confidently, and now have the muscular strength to turn somersaults and complete a standing broad jump.
- 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.