Growth and Development, Ages 1 to 12 Months

Babies usually grow in natural, predictable steps, moving from one milestone to the next. During the first year you will see gains in five major areas:

• Reference Physical development. Babies steadily gain weight and grow in length throughout this first year, often in Reference growth spurts Opens New Window.
• Reference Cognitive development. This means how the brain forms its abilities to learn and remember. Babies soon begin to recognize familiar people. They gradually realize that people and objects exist even when they are out of sight. They begin to connect what is seen with what is tasted, heard, and felt.
• Reference Emotional and social development. Babies form bonds with their parents and other caregivers. When cared for in a loving and consistent way, most babies begin to engage and interact with others.
• Reference Language development. Babies start communicating with different types of cries, then progress to babbling. For more information, see the topic Reference Speech and Language Development.
• Reference Sensory and motor skill development. As your baby's brain, nerves, and muscles continue to grow, controlled movements become more refined, and Reference newborn reflexes gradually fade.

Milestones by age

Each baby grows and gains skills at his or her own pace. It's common for a baby to be ahead in one area, such as language, but a little behind in another.

By around 2 months, most babies:

• Smile as a way to engage others.

By 4 months, most babies:

• Start using their arms with purpose. For example, babies may move their arms and squirm when excited or "swipe" at dangling objects.

By 6 months, most babies:

• Have doubled their birth weight.
• Are able to sit with little or no support.

By 9 months, most babies:

• Get upset when you or another caregiver leaves.
• May have begun to crawl.

By Reference 12 months, most babies:

• Have tripled their birth weight.
• Are expressive and have formed a close attachment to their parents.
• Understand some words and begin to figure out the meaning of many others.
• May be able to say a few words.
• May be walking.

Reference Premature infants Opens New Window typically reach milestones later than others of the same age. But they are usually on schedule for their expected time of birth. For example, a baby born 2 months early might reach milestones 2 months later than a full-term baby born at the same time.

Healthy babies who were born prematurely usually reach normal developmental levels for their age by the time they are about 24 months of age. Learning and thinking skills usually are first to catch up. Reference Motor skills Opens New Window are often the last to catch up.

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