Children develop the muscular control and concentration to master some precise hand and finger movements during their fourth year of life. Most can now grasp crayons and pencils with the thumb on one side and fingers on the other, as adults do, and can trace squares, copy circles, and draw a person with two to four body parts.
- 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.