Newborn infants sleep in a fragmented fashion in periods lasting 2 to 5 hours, occurring throughout the day and night. These newborns will typically awaken for 1 to 3 hours when they desire to feed. By 8 to 12 weeks of age, these rather short sleep periods become consolidated and more sleep occurs at night.
Thankfully for sleep-deprived parents, babies begin to sleep for 8-hour periods at night by the age of 4 to 6 months. This nighttime sleep may be disrupted by awakenings that might occur 5 or 6 times. (Often, it is necessary to allow children to fall back asleep on their own when this occurs, rather than provoking sleep-onset behavioral insomnia by always comforting them back to sleep.) They will continue to nap during the day for 2 to 4 hours.
By 12 months, your child will sleep for eight hours at night and nap one or two times per day. These naps may shorten, only lasting 1 to 2 hours.
As your baby continues to grow and develop, his or her sleep needs will continue to change as well.
Durmer, JS et al. "Pediatric Sleep Medicine". Continuum. Neurol 2007; 13(3):153-200.