Babies usually progress in a natural, predictable sequence from one developmental milestone to the next. During the first year you will see gains in five major areas.

• Physical development is rapid during the first year of life. Babies steadily gain weight and grow in length throughout this first year. Your baby's birth weight doubles around 6 months of age and triples by about 12 months. But remember that each child is different. Your child may be smaller or larger than other children of the same age. As long as your child continues to grow at a regular pace, your doctor will likely assure you that your baby's growth is within the normal range. Most babies nearly triple their birth weight by their first birthday.
• Cognitive development, or how the brain develops its abilities to learn and remember, progresses rapidly. Babies soon begin to recognize familiar people. As their memory develops, they gradually realize that people and objects exist even when they are out of sight, a cognitive skill called object permanence. Sensory integration evolves throughout the first year, which is the process by which a baby's brain begins to connect what is seen with what is tasted, heard, and felt.
• Emotional and social development begins with the bonds babies form with their parents and other caregivers. When cared for in a loving and consistent way, most babies begin to engage and interact with others. By 2 months of age, your baby smiles as a way to engage you. This is called a "social smile." At about 9 months, your baby gets upset when you or another caregiver leaves. This is a normal phase that is known as separation protest. By 12 months, most babies are expressive and have formed a close attachment to their parents. They also experience some degree of separation protest.
• Language development occurs along with brain growth. Babies start communicating with different types of cries, then progress to babbling. By 12 months, they may be able to say a few words. Most babies also understand some words by this time and begin to infer the meaning of many others. For more information, see the topic Speech and Language Development.
• Sensory and motor skill development progresses with the continual growth of the brain, nerves, and muscles. As controlled movements become more refined, newborn reflexes gradually fade. By 4 months of age, your baby will start using the arms with purpose. For example, your baby may move the arms and squirm when excited or "swipe" at dangling objects. By 6 months of age, your baby will likely be able to sit with little or no support. Your baby learns to crawl usually by 8 months of age. Some babies will be walking by their first birthday.