Chapter 2 – The Mechanisms of Children's Sleep

How many hours of sleep does a baby need in a day? How long should it take them to fall asleep? How many night awakenings are normal?
It’s impossible to find a single, universal answer to these questions. All studies that have tried to establish a precise rule to address parents’ doubts about their children’s sleep patterns have encountered one clear limitation: the wide individual variability in sleep habits.

Total sleep duration, the number of daytime naps and night awakenings, and the time it takes to fall asleep evolve rapidly during the first months of life and differ significantly from child to child. These patterns are partly determined by innate characteristics—often inherited from the parents—and partly by environmental factors, such as the cultural approach to sleep in the child’s society and the family’s habits.

Taking this variability into account, we can say approximately (7) that during the first three months of life, about half of infants sleep between 13 and 16 hours each day, combining nighttime sleep and naps. From six months to one year of age, half of children sleep between 12 and 16 hours a day.

Initially, sleep is divided into short naps spread evenly between day and night. Gradually, however, sleep tends to concentrate more and more during nighttime hours. At six months, most babies sleep at least five consecutive hours at night—but many still don’t. By one year of age, 15% of children still sleep less than five uninterrupted hours per night.

Children’s sleep is one of the topics that most concerns parents. According to a recent study published on PuBMed, 40% of parents of an eight-month-old baby believe their child has a sleep disorder (8). It’s understandable to be puzzled by such unpredictable and uncontrollable behavior, and in some cases, there are indeed sleep disorders or other health issues that interfere with a child’s rest.

If parents are concerned, it is always appropriate to consult a pediatrician. However, in most cases, they will find that their child’s seemingly unusual behavior falls within the wide—and completely normal—range of infant sleep habits.

To help alleviate unnecessary concerns, it’s useful to understand how children’s sleep works and how it differs from adult sleep.

Sleep is not a uniform state of brain quietude. It consists of cycles of phases in which the brain is active in different ways. Science has long studied these phases to clarify their function. When adults fall asleep, we initially enter a light sleep phase, followed by deep, dreamless sleep. Finally, we enter active sleep, known as the REM phase (Rapid Eye Movements), during which the eyes move rapidly under closed eyelids, indicating that the person is dreaming. Each full sleep cycle lasts 90–100 minutes. Then we briefly wake up and immediately fall back asleep, starting a new cycle. Usually, we don’t even remember these brief awakenings. We only fully wake up when we’ve slept enough—or when, unfortunately, the alarm rings.

When a baby falls asleep (9), however, they enter directly into the REM phase, which occupies 50%, sometimes up to 75%, of their sleep cycle—compared to 20% in adults. Researchers have hypothesized that REM sleep is essential for the baby’s brain to test and regulate the connections between different brain areas, thus supporting nervous system maturation.

During REM sleep, babies may move, kick, make noises, and even briefly open their eyes, giving parents the impression they are awake. Picking them up during this phase may actually wake them. That’s why it’s best to be sure the baby is truly calling for attention before intervening.

After REM sleep, the baby enters a phase of deep, dreamless sleep. At the end of this, they complete a sleep cycle—which, in the first months of life, lasts about 50–60 minutes—and they wake up. Unlike adults, who briefly awaken between cycles without being aware of it, babies are fully alert for a few moments. They assess their sensations and the surrounding environment: Are they hungry? Do they feel well or is something bothering them? Do they feel safe or is there something unfamiliar? Are they breathing properly?

If everything feels okay, the baby will usually fall back asleep just like an adult. But often, something catches their attention and, instead of closing their eyes again, they call for mom or dad’s help.