Infant development can be separated into four areas: small motor development, large motor development, social development and language development, explains the American Pregnancy Association. Small motor development pertains to eye-hand coordination, while large motor development relates to actions such as sitting or walking. Social development is about a baby's response to faces and voices. Language development references a child's ability to understand language and speak.

In the first month of life, a newborn usually turns her head from side to side, quiets when hearing a voice and has a strong grasp reflex, states the American Pregnancy Association. In the second month, an infant typically follows a dangling object with her eyes, lifts her head 45 degrees when lying on her stomach and gives a social smile in response to various stimuli.

In the third month of development, a baby often demonstrates awareness of being in an unfamiliar environment, holds objects, bears some weight on legs and tries to talk to communicate, according to the American Pregnancy Association. In the fourth month, a child frequently begins drooling, laughs and rolls from back to side. The fifth month brings rolling from stomach to back, teething and toe playing.

A baby in the sixth month says one-syllable sounds and pulls her feet to her mouth, while the average baby in the seventh month sits without support and responds to her name, notes the American Pregnancy Association. In the eighth month, an infant begins combining syllables and dislikes having a diaper change. A baby in the ninth month often begins crawling and responds to simple verbal commands.