In•fant \’in-fənt\


Definition: 1. A child in the first period of life, 2. A person who is not of full age:  MINOR (Merriam-Webster Online)

Birth–18 months

Physical Development

  • Immediately after birth an infant will normally lose some baby weight, but after 2 weeks the infant starts gaining weight quickly. By 4 to 6 months, the infant’s weight should be about double its birth weight.
  • The head and neck of a newborn account for about 30% of its total body volume. In an adult, the head and neck account for about 10% of our total body volume.
  • An infant’s physical characteristics change rapidly.  Until about 2 months of age, a newborn cannot support its head or control its hands or feet.  This changes by 4 months when an infant can begin to manipulate its hands and feet, and the neck muscles are strong enough to hold the head upright.
  • By 9 months, the infant may have begun to crawl, can possibly walk with support from an adult, and can sit without support for a long period of time. At one year, the infant may be able to stand and begin to walk alone.
  • Synaptic overproduction and loss, a process in which neurons are produced quickly and pared away, is a critical aspect of brain development. This process is most active during the first year of life, but can extend into adolescence. Different brain regions appear to develop at different rates. For example, neuronal development in the visual area of the brain peaks halfway through the first year and reaches adult levels around the end of preschool.

Cognitive Development

  • Some heritable genetic disorders that cause cognitive impairment can be prevented.  For example, damage due to phenylketonuria, a heritable disorder that leads to mental disability, can be completely prevented by  following a strict diet avoiding the amino acid phenylalanine, which is found in many foods including eggs and milk.
  • Infants have a surprisingly sophisticated understanding of the world. At less than a month of age an infant can imitate another’s gestures and by nine months may learn new behaviors through simple observation. For instance, infants have remembered how to unlock a container up to 24 hours after watching a peer do it.
  • Loving care-giving can enhance certain neurochemicals—such as serotonin and thyroid hormones—that help regulate distress and pain.  This has been shown to affect a person’s brain chemistry throughout his or her life.
  • Infants raised in a healthy environment—with access to quality education, care giving and nutrition— score significantly higher on IQ tests. In contrast, infants raised around harmful toxins—such as cigarette smoke and polluted air—are more likely to experience cognitive impairment later in life.

Emotional, Cultural, and Social Development

  • By 6 to 9 months, infants are interacting with their social environment. Babies will smile and babble at other babies, and sometimes initiate or return social bids. By 9 to 12 months, infants will imitate each other as a simple form of play.
  • Children tend to say their first words at between 10 and 15 months. Following this, they learn that words can be broken into parts, such as how “shoes” can be broken into “shoe” + “s”, eventually combining words into meaningful phrases.

Next: Toddler