The learning process becomes more thoughtful for toddlers as they approach their third birthday. They begin solving problems and performing mental trial-and-error instead of manipulating objects physically. As their understanding of cause and effect deepens, toddlers become more interested in mechanical toys and turning lights and appliances on and off.
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.