The rate of behavioral, social, and intellectual development varies considerably from infant to infant. Some infants develop faster, although certain patterns may run in families, such as late walking or talking. Environmental factors, such as lack of sufficient stimulation, can slow development; conversely, stimulation can hasten development. Physical factors, such as deafness, can also slow development. Although a child's development is usually continuous, temporary pauses may occur in the development of a particular function, such as speech.

Crying is one means of communication. Infants cry because they are hungry, uncomfortable, distressed, and for many other reasons that may not be obvious. Infants cry most—typically 3 hours a day—at 6 weeks of age, usually decreasing to an hour a day by 3 months of age. Parents generally offer crying infants food, change their diaper, and look for a source of pain or discomfort. If this does not work, holding or walking with the infant sometimes helps. Occasionally nothing works. Parents should not force food on crying infants, who will readily eat if hunger is the cause of their distress.

An Infant's First Year: Developmental Milestones Age Milestone 1 month Brings hands toward eyes and mouth Moves head from side to side when lying on stomach Follows an object moved in an arch about 6 inches above face to the midline (straight ahead) Responds to a noise in some way, such as startling, crying, or quieting May turn toward familiar sounds and voices Focuses on a face 3 months Raises head 45 degrees (possibly 90 degrees) when lying on stomach Opens and shuts hands Pushes down when feet are placed on a flat surface Swings at and reaches for dangling toys Follows an object moved in an arch above face from one side to the other Watches faces intently Smiles at sound of mother's voice Begins to make speechlike sounds 5 months Holds head steady when upright Rolls over one way, usually from stomach to back Reaches for objects Recognizes people at a distance Listens intently to human voices Smiles spontaneously Squeals in delight 7 months Sits without support Bears some weight on legs when held upright Transfers objects from hand to hand Looks for dropped object Responds to own name Babbles, combining vowels and consonants Wiggles with excitement in anticipation of playing Plays peekaboo 9 months Works to get a toy that is out of reach Objects if toy it taken away Crawls or creeps on hands and knees Pulls self up to standing position Stands holding on to someone or something Says “mama” or “dada” indiscriminately 12 months Gets into a sitting position from stomach Walks by holding furniture; may walk one or two steps without support Stands for a few moments at a time Says "dada" and "mama" to the appropriate person Drinks from a cup Claps hands and waves bye-bye

Last full review/revision November 2006 by Ruth A. Lawrence, MD