Every child’s sleep needs are slightly different, and this may be largely determined by genetics and other factors. The important consideration is that your child obtains enough sleep to feel rested, happy, and healthy. The average sleep needs presented here are just that -- averages -- and your child may normally require more or less sleep. In general, younger children may sleep during the day and night, and as they get older they will sleep more at night and require fewer naps.
The sleep needs of children can be summarized this way:
Newborns sleep in episodes that last 2 to 5 hours. They then will awake for 1 to 3 hours to feed. These periods are scattered across the day and night, due to a lack of a circadian rhythm. By 8 to 12 weeks of age, the periods of sleep become more consolidated and occur more frequently at night.
4 to 6 Months Old
Infants who are 4 to 6 months old typically sleep eight hours overnight, with multiple brief awakenings. These awakenings may draw parents' attention, but the infants should be allowed to fall back asleep so that they do not develop sleep-onset insomnia. Infants may take two or three prolonged naps during the day that last 2 to 4 hours.
12 Months Old
By the time your child is 12 months old, they will continue to sleep eight hours at night. One-year-olds may take shorter naps a few times per day, often in the late morning or early afternoon, that last 1 to 2 hours.
18 Months Old
Children who are 18 months old may on average sleep 8 to 10 hours per night and take one nap. The single daytime nap may last 1 to 2 hours.
Those children who are transitioning into preschool or daycare, typically in the age range of 3 to 5 years, require 11 to 12 hours of sleep per night on average. They will often continue taking daily naps. Many in this group will stop napping as they enter kindergarten.
Children who are 6 to 12 years old, often advancing through elementary and even middle school, will typically sleep on average 10 to 11 hours per night. Naps are no longer appropriate in this age group. For those children who continue to nap, there may be an underlying sleep problem or medical condition that should be evaluated by your pediatrician.
Durmer, JS et al. "Pediatric Sleep Medicine". Continuum. Neurol 2007; 13(3):153-200.