The infancy stage is from birth to one year. In the first few months of life, babies spend much of their time sleeping. A lot of growth happens while sleeping. When not sleeping, young infants eat every 2-4 hours, and spend a little time observing their surroundings.

Later in infancy, babies will still sleep for 2-6 hours a day, drink formula or breast milk, and now they will begin to eat solid foods multiple times a day. older babies are also more active, engaging in play more often throughout the day, and interacting with adults around them.

In early infancy, some cognitive milestones babies will meet are recognizing family members and familiar people, smiling when they recognize a familiar face or voice, learning to make eye contact, and reacting to unfamiliar faces or voices by crying.

As babies reach the later stage of infancy, they begin to develop more cognitively. For example, they will start to show emotions such as getting upset when a toy is taken away. They will start to show interest in games such as pat-a-cake, or clapping. They begin to be able to imitate the actions of caregivers and parents at this age as well.

The beginning stages of language development in infancy consist mostly of crying, small giggles, and cooing. Cooing is the expression of short vowel sounds. Babies may have different cries for different needs, even at a young age.

As babies grow, so does their expression of language. Older infants are able to say simple words such as "mama' and "dada". By 9-10 months, they know who "mama" and "dada" are. As they reach the 1 year mark, they will be able to imitate object and animal sounds. They will also begin to be able to nod and shake their head for "yes" and "no".