As babies approach their second year of life, they show sustained preferences for the mother and/or regular caregiver above all others. Although they still enjoy the company of other people, children at this age will choose their primary caregivers if they have the option. Babies will seek their primary caregivers for comfort when distressed, for food when hungry, and for play. Sometimes, a baby might even wake up and look for her primary caregiver in the middle of the night.
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.