By 2 months:

Social and Emotional:

Begins to smile at people
Can briefly calm themselves (may bring hands to mouth and suck on fist, fingers, parts of the hand)
Tries to look at parent when heard

Language and Communication:

Coos; makes gurgling sounds
Turns head toward sounds

Cognitive (learning, thinking, problem-solving):

Pays attention to faces (lips and eyes mostly)
Begins to follow things with eyes and recognize people at a distance
Begins to act bored (cries, fussy) if activity doesn’t change

Movement and Physical Development:

Can hold head up and begins to push up when lying on stomach
Makes smoother, less rigid movements with arms and legs

By 4 months:

Social and Emotional:

Smiles spontaneously, especially at people
Likes to play with people and may cry when playing stops
Copies some movements and facial expressions, like smiling or frowning

Language and Communication:

Begins to babble
Babbles with expression and copies sounds they hear
Cries in different ways to show hunger, pain, or sleepiness

Cognitive (learning, thinking, problem-solving):

Can express happy and sad emotion
Responds to affection
Reaches for toy with one hand
Uses hands and eyes together, such as seeing a toy and reaching for it
Follows moving things with eyes from side to side
Watches faces closely
Recognizes familiar people and things at a distance

Movement and Physical Development:

Holds head steady, unsupported
Pushes down on legs when feet are on a hard surface
May be able to roll over from tummy to back
Can hold a toy and shake it and swing at dangling toys
Brings hands to mouth
When lying on stomach, pushes up to elbows

By 6 months:

Social and Emotional:

Definitely knows familiar faces and begins to recognize strangers as unknown persons
Likes to play with others, especially parents
Responds to other people’s emotions and often seems happy
Likes to look at self in a mirror

Language and Communication:

Responds to sounds by making sounds
Strings vowels together when babbling (“ah,” “eh,” “oh”) and likes taking turns with parent while making sounds
Responds to own name
Makes sounds to show joy and displeasure
Begins to say consonant sounds (jabbering with “m,” “b”)

Cognitive (learning, thinking, problem-solving):

Looks around at things nearby
Brings objects to mouth
Shows curiosity about things and tries to get things that are out of reach
Begins to pass things from one hand to the other

Movement and Physical Development:

Rolls over in both directions (front to back, back to front)
Begins to sit without support
When standing, supports weight on legs and might bounce
Rocks back and forth, sometimes crawling backward before moving forward

Feedings:

breastmilk, formula from bottles, plain infant rice cereal or infant oatmeal cereal


By 9 months:

Social and Emotional:

May be afraid of strangers
May be clingy with familiar adults
Has obvious favorite toys

Language/Communication:

Understands “no”
Makes a lot of different babbling sounds like “mamamama” and “bababababa”
Copies sounds and gestures of others
Can use fingers to point at things

Cognitive (learning, thinking, problem-solving):

Watches the path of something as it falls
Looks for things they see you hide
Passively Plays peek-a-boo
Puts things in their mouth
Moves things smoothly from one hand to the other
Picks up things like cereal pieces between thumb and index finger

Movement and Physical Development:

Stands unsteadily, holding on to furniture or parent (may unexpectedly 'fall' while standing for no apparent reason)
Can get into sitting position
Sits without support
Pulls to stand
Crawls

Feedings:

breastmilk, formula, infant rice or oat cereal, pureed fruits, pureed vegetables, plain Greek yogurt
Sippy cup should be introduced and used