In the delivery room, the pediatrician talks about a newborn. Three weeks later, the health record refers to an infant. At the local maternal and child health clinic, staff may start talking about a young child from six months of age. These terms are not interchangeable: the distinction between them determines the type of medical follow-up, dietary recommendations and warning signs used by healthcare professionals.
Understanding the WHO definition of an infant helps pinpoint the stages of the first few months and identify which recommendations apply to each age group.
Newborn, infant, young child: WHO age thresholds
The WHO defines a newborn as a child under 28 days old. This neonatal period carries the highest risks: in 2019, around one-third of newborn deaths occurred on the day of birth, and nearly three-quarters during the first week of life.
After the first 28 days, the infant period begins and lasts until the end of the first year. The Dictionary of the Académie française sets a slightly different age range—from three weeks to two years—which often creates a gap between international medical terminology and everyday usage in France.
In WHO publications, the term “young child” is used for the one-to-five age group. This distinction is more than cosmetic: it determines which mortality indicators, growth charts and vaccination protocols apply.
Why the neonatal period is treated separately from the rest of the first year
The first 28 days are marked by specific conditions linked to a lack of quality care at birth, including asphyxia, infections and complications of prematurity. In 2019, neonatal deaths accounted for nearly half of all deaths among children under five.
Grouping newborns and infants together would obscure these realities. That is why public health programs consistently separate the two periods in their statistics and care protocols.
Infant feeding: what WHO recommendations mean in practice
The WHO and UNICEF recommend initiating breastfeeding within one hour of birth, followed by exclusive breastfeeding for the first six months. From six months, safe, nutritionally appropriate solid complementary foods should be introduced alongside breast milk. Breastfeeding can continue until the child is two years old or beyond.
It might seem that these recommendations apply only to low-income countries. They are relevant in every setting. Nearly 400,000 deaths among children under five could be prevented each year if all infants were exclusively breastfed for six months, with breastfeeding continuing until age two or beyond.
The gap between feeding recommendations and commercial products
An analysis by the Access to Nutrition Initiative highlights a practical issue: European regulations on baby foods do not always align with WHO recommendations. Some products marketed for infants use health claims or product names that can confuse parents.
In practice, this means that a product legally marketed for a four-month-old infant may conflict with the recommendation to breastfeed exclusively until six months. Staff at maternal and child health clinics regularly encounter this confusion during appointments.
Postnatal care for infants: mother and child at the heart of care
WHO recommendations on postnatal care are not limited to the baby. They explicitly include the mother’s physical and mental health in the weeks after birth. This mother-and-child approach changes how follow-up care is organized.
- For premature or low-birth-weight babies, the WHO recommends starting kangaroo care (skin-to-skin contact) as soon as possible after birth, without waiting for the baby to be fully stabilized.
- Checking for danger signs in newborns—such as breathing difficulties, hypothermia or refusing to feed—is an integral part of every postnatal appointment.
This framework explains why infant care in France includes mandatory examinations from the first few days, with frequent checkups during the neonatal period, followed by monthly visits throughout the first year.
Prematurity and the limits of the definition: when corrected age makes a difference
The WHO definition is based on chronological age, calculated from the day of birth. For a full-term baby, this poses no problem. For a premature baby, corrected age adjusts developmental milestones to account for the weeks the baby was born early.
Using the same assessment charts without adjusting for prematurity can lead to unnecessary concerns or, conversely, to a genuine delay being missed. This nuance is not included in the official definition of an infant, but it shapes the entire course of pediatric follow-up.
What the official definition leaves open
The upper age limit for the infant period varies by source: twelve months according to the WHO, and up to twenty-four months in everyday French usage and according to the Académie française. This lack of precision has practical implications for how long certain enhanced monitoring protocols apply, particularly those aimed at preventing sudden unexpected infant death.
These classifications are primarily used to shape public health policies. Knowing these age thresholds helps parents understand why medical follow-up changes pace after the first month and again after the first birthday. Each transition reflects a real change in the baby’s risks and needs.
