It takes some time before young children can grasp the meanings of words that describe physical relationships. But during the third year, words such as under, over, and in will begin to make more sense.
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.