Please understand that each child developes at a different rate...
...these are simply guideline milestones
Social Development Skills
0-3 months =  Turns head towards a speaking voice. Recognizes primary caregiver. Bonds to primary caregiver. Finds comfort in the human face. Displays a social smile. Is quieted by a voice. Begins to differentiate self from caregiver.
4-6 months =  Seeks out adults for play by crying, cooing, or smiling. Responds with entire body to familiar face by looking at the person, smiling, kicking and waving. Participates actively in interactions with others by vocalizing in response to adult speech. Smiles at familiar faces and stares solemnly at strangers. Distinguishes between familiar and unfamiliar adults and surroundings.
7-9 months =  Becomes upset when separated from a favorite adult. Acts deliberately to maintain the presence of a favorite adult by clinging or crying. Uses adults as a base for exploration, typically. Looks to others who are exhibiting signs of distress. Enjoys observing and interacting briefly with other children. Likes to play and responds to games such as patty-cake and peek-a-boo. Engages in solitary play. Develops preferences for particular people and objects. Shows distress when in the presence of a stranger.
10-12 months = Shows a decided preference for one or two caregivers. Plays parallel to other children. Enjoys playing with siblings. Begins asserting self. Begins developing a sense of humor. Develops a sense of self-identity through the identification of body parts. Begins distinguishing boys from girls. 
13-18 months =  Demands personal attention. Imitates behaviors of others. becomes increasingly aware of the self as a separate being. Shares affection with people other then primary caregiver. Shows ownership of pssessions. Begins developing a view of self as autonomous when completing tasks independently.
19-24 months =  Shows enthusiasm for company of others. Views the world only from own, egocentric perspective. Plays contently alone or near adults. Engages in functional play. Defends possessions. Recognizes self in photographs and mirrors. Refers to self with pronouns such as "I" or "me". Categorizes people by salient characteristics such as race or hair color. Shows less fear of strangers.
25- 36 months =  Observes others to see how they do things. Engages primarily in solitary or parallel play. Sometimes offers toys to other children. Begins to play cooperatively with other children. Engages in sociodramatic play. Wants to do things indepently. Asserts independence by using "no" a lot. Develops a rudimentarty awareness that others have wants or feelings that may be different than their own. Makes demands of or "bosses" parents, guardians and caregivers. Uses physical aggression less and uses words to solve problems. Engages in gender sterotypical behavior.
Language Development
Cognitive Development
Emotional Development
Social Development
Physical Development