A baby is considered an infant from birth through 12 months of age. The term “infant” covers the entire first year of life, including the newborn stage. After the first birthday, children are typically reclassified as toddlers.
That said, the word “infant” gets used differently depending on context. Medical providers, product safety regulators, and developmental researchers each draw slightly different lines, which can make things confusing when you’re reading labels, filling out forms, or talking to your pediatrician.
Newborn vs. Infant: The First Distinction
The neonatal period, commonly called the newborn stage, covers the first four weeks of life. A baby who is four weeks old or younger is a neonate. After that four-week mark, they’re still an infant but no longer a newborn. This distinction matters in medical settings because the first 28 days involve a unique set of health considerations, from umbilical cord care to screening tests.
In everyday conversation, most people use “newborn” loosely for the first two or three months. Pediatricians are more precise: newborn means under four weeks, and infant covers the full span from birth to one year.
When Infancy Ends and Toddlerhood Begins
The transition from infant to toddler happens around the first birthday. The CDC groups infants and toddlers together as ages zero to three for general guidance, but the shift in terminology typically lines up with a child beginning to walk. The word “toddler” itself comes from “toddle,” referring to those early, unsteady steps.
There’s no single day when your baby officially becomes a toddler. Some children walk at 9 months, others closer to 15 months. For medical records and developmental screening, though, 12 months is the standard cutoff.
How Product Safety Uses Age Labels
If you’ve noticed age labels on cribs, car seats, and toys, those follow guidelines from the U.S. Consumer Product Safety Commission (CPSC). The CPSC uses 18 months as a key dividing line for toy safety testing. Products intended for children 18 months or younger undergo stricter impact and stress testing than those designed for older toddlers. For example, a toy for an infant must survive 10 drops from 4.5 feet, while a toy for an older toddler is tested with only 4 drops from 3 feet.
Small parts regulations apply to all children under three years of age, which is why you’ll see “not for children under 3” on so many packages. And any product designed to help with sleeping or feeding for children three and younger falls under the federal definition of a “child care article,” which triggers additional safety requirements.
What Changes During the First Year
The infant period involves the fastest physical growth a person will ever experience. A baby’s heart rate actually peaks around one month of age at roughly 145 beats per minute, then gradually slows. Their breathing rate starts at about 44 breaths per minute at birth and steadily declines, with the steepest drop happening before age two. These numbers are far higher than adult ranges, which is normal and expected.
Developmentally, the first 12 months bring a remarkable sequence of milestones: social smiling, rolling over, sitting without support, babbling, responding to their name, and in many cases, pulling to stand or taking first steps. The CDC tracks these milestones at 2, 4, 6, 9, and 12 months as checkpoints for healthy development.
Feeding Milestones During Infancy
For roughly the first six months, infants rely exclusively on breast milk, formula, or a combination of the two. Around six months, you can start introducing solid foods. These early foods are considered “complementary,” meaning they add to milk or formula rather than replace it. Most infants continue drinking breast milk or formula alongside solid foods through the end of the first year and often beyond.
Sleep Safety Throughout the Infant Period
Safe sleep recommendations apply for the entire infancy period and beyond. Infants should be placed on their backs for every sleep, including naps. The sleep surface should be firm and flat, in a safety-approved crib or bassinet, with no blankets, pillows, bumper pads, or soft toys. Ideally, the baby’s sleep area stays in the same room as the parents for at least the first six months. Weighted sleep products, including weighted swaddles and sleep sacks, are not considered safe for infants at any age.
Vaccination Schedule in the First Year
The infant vaccination schedule is concentrated at a few key ages. The first dose of hepatitis B is given at birth. At two months, infants receive their first round of several core vaccines, covering rotavirus, diphtheria, tetanus, pertussis, pneumococcal disease, and polio. Second doses follow at four months, with additional doses at six months. By the time a child reaches 12 months, they’re due for vaccines against measles, mumps, rubella, chickenpox, and hepatitis A. These visits are typically combined with developmental screening and growth tracking, making them some of the most important appointments of the first year.