At 4 months, babies begin coordinating their emerging perceptive abilities to struggle to get objects that are out of reach. They use their developing motor skills to grasp items, roll over, or sit up. Babies’ growing curiosity and abilities lead them to try new things, so parents and caregivers should arrange the environment to minimize the possibility of falls, bumps, and bruises that can result from unexpected new movements. Also, babies at this age should never be left alone on a changing table, bed, couch, or other item to prevent dangerous falls.
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.