A 6-month-old is put down to sleep at 6:30 p.m. and wakes up at 11:30 p.m. for a feeding. The infant sings, coos and vocalizes for an hour before falling back to sleep. And the parents are left to wonder if this behavior is normal and whether the baby will outgrow it.

The simple answer to both questions is yes. But other things do come into play.

Parental concerns regarding sleep issues are universal, and anxieties related to infant bedtime struggles and nighttime awakening are reported in one-third of all families. It is important that parents understand there is a broad range of normal behavior and that the norm changes dramatically as infants move through developmental stages.

Nighttime awakening is natural for both infants and adults as they pass through a number of sleep cycles, moving into very deep sleep for the first two or three hours before cycling between lighter (dreaming) sleep and deeper sleep. It is normal to wake up during these periods of light sleep.

The 6-month-old who settles easily when put down for the night and amuses himself when he awakens will often surprise mom and dad a few months later with tears at bedtime and fussiness during the night, as transitions to sleep become an issue. While this behavior is common, all parents worry that something is wrong - perhaps a fever, an infection or an undiagnosed pain or illness? While these are questions parents should consider, in general, the behavior change is the beginning of a new developmental stage.

Between 6 and 12 months of age, infants develop what psychologists call "object permanence." Previously, a favorite toy that was out of sight was out of mind. At this age, babies have learned that the toy exists, even when they can't see it, and will search and cry until they have it. They have also learned that those nice people who feed, cuddle, change and play with them are somewhere when they're not with them. Knowing this makes them anxious, even angry, because they are alone and want company.

Armed with the knowledge that this behavioral change is normal and expected, parents can contain the situation while avoiding guilt and anxiety. In many cases, the babies are already overstimulated and will benefit more from the calming presence of a quiet mom or dad than from the food, drink, bright lights or play that reward and encourage fussy behavior.

Since infants thrive in a consistent, structured environment, parents can encourage healthy infant sleep habits by maintaining a consistent schedule. Cuddle or rock the baby before bed, but put him down while he is still awake. This will allow him to learn how to settle himself by sucking a thumb or playing with a favorite blanket or stuffed animal. Parents may stay in the room, without making eye contact, while the infant settles down. After a few minutes, the touch of a parent's hand may also help the baby settle.

When infants wake up at night, a parent's presence can be reassuring, but avoid the overstimulation caused by turning on the lights or feeding. Babies over the age of 6 months do not awaken in the night because they are hungry, and holding and cuddling fussy, uncomfortable infants will not spoil them.

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Dr. Edward Bailey is chief of pediatrics at NSMC North Shore Children's Hospital, on staff at Mass General Hospital for Children and a father of three. You can contact him at ebailey@aap.org.'