Social Development Milestones 0-3 Years: What the Research Says

The first three years of life are
the most remarkable period of social
development in the entire human lifespan.
In just thirty-six months — a child
transforms from a newborn who cannot
distinguish self from other to a three-year-old
who forms genuine friendships, understands
others’ emotions, engages in cooperative
pretend play, and navigates the complex
social world of the family and peer
group. Research on social development
milestones in the first three years
provides specific, evidence-based guidance
about what is typical at each stage —
and what parents can specifically do
to support this extraordinary development.

This article covers what the research
shows about social development milestones
from birth to three years — what
to expect, what supports development,
and what parents can specifically do.

Why the First Three Years Matter
Most for Social Development

Research on social development and
early experience — including significant
work by Jack Shonkoff at Harvard’s
Center on the Developing Child —
finds that the first three years are
the most sensitive period for social
development for several specific reasons:

Brain development is most rapid.
Research finds that the brain
develops more rapidly in the
first three years than at any
other period — with the social
brain regions — prefrontal cortex,
amygdala, and limbic system —
particularly active and sensitive
to social experience.

Attachment forms in the first year.
Research by Bowlby and Ainsworth
finds that the attachment relationship —
the foundation of all subsequent
social development — is established
in the first year of life.
The quality of early attachment
has lasting effects on social
development, mental health,
and relationship quality throughout life.

Early social experience shapes
the developing brain. Research
on serve-and-return interaction —
the back-and-forth exchanges
between infant and caregiver —
finds that these interactions
literally shape the developing
social brain — building the
neural connections that social
competence requires.

Birth to Three Months —
The Social Newborn

Research on newborn social development
finds that babies are social beings
from birth — with specific capacities
for social engagement that form the
foundation of all subsequent development.

Social milestones:
Preference for faces — particularly
the primary caregiver’s face — from birth.
Turning toward voices — particularly
the primary caregiver’s voice — from birth.
Quieting and alerting to social
stimulation — from birth.
Social smiling — genuine smiling
in response to a social partner —
emerging at approximately six weeks.
Beginning protoconversation —
turn-taking vocal exchanges
with caregivers — from approximately two months.
Eye contact — sustained mutual
gaze with caregivers — from approximately six weeks.

What parents can do:
Respond consistently and warmly
to the baby’s communications.
Make frequent warm eye contact.
Talk, sing, and coo — responding
to the baby’s vocalizations.
Hold and physically comfort consistently.

Research finding: the quality
of caregiver responsiveness
in the first three months is
one of the strongest predictors
of secure attachment and social development.

Three to Six Months —
Social Engagement Deepens

Research on social development
between three and six months finds
significant developments in social engagement:

Social milestones:
Consistent, joyful social smiling
— smiling reliably in response
to familiar faces.
Laughing — emerging at approximately four months.
Expressing pleasure and displeasure
clearly — through facial expression and vocalization.
Differentiating familiar from
unfamiliar people — showing
preference for familiar caregivers.
Reciprocal social play —
engaging in back-and-forth
social games — peekaboo, tickling.
Reaching toward familiar people.

What parents can do:
Engage in face-to-face social
play — responding to the baby’s expressions and vocalizations.
Play reciprocal games — peekaboo,
hide and seek with faces.
Narrate what you are doing —
building the serve-and-return interaction that brain development requires.

Six to Nine Months —
The Social World Expands

Research on social development
between six and nine months finds
several significant milestones:

Social milestones:
Stranger anxiety emerges —
distress in the presence of
unfamiliar people — from approximately eight months.
Separation anxiety begins —
distress when separated from
the primary caregiver.
Social referencing begins —
looking to the caregiver for
emotional information about
novel situations — from approximately nine months.
Recognizing emotional expressions —
responding differently to happy,
sad, and angry faces.
Beginning intentional communication —
using gestures and vocalizations
to communicate with social partners.

What parents can do:
Respond warmly to stranger
anxiety — rather than forcing
social interaction.
Handle separation warmly and
consistently — brief separations
with warm reunions build security.
Follow the baby’s gaze and
attention — and respond to
social referencing.

Nine to Twelve Months —
Joint Attention and Social Learning

Research on social development
between nine and twelve months identifies
one of the most significant social-cognitive
milestones of infancy:

Social milestones:
Joint attention emerges —
the shared focus of infant
and caregiver on the same
object or event — from approximately nine to twelve months.
Pointing — both declarative
pointing — “look at that!” —
and imperative pointing —
“I want that!” — emerges.
Imitation of social actions —
waving, clapping, simple gestures.
Beginning of intentional social
communication — using gestures,
vocalizations, and eye contact
to communicate intentionally.
Showing objects to caregivers —
sharing interest and experience.

What parents can do:
Follow the baby’s point and
gaze — and name what they
are interested in.
Respond to showing — “Yes —
that’s a dog! Woof woof!”
Play imitation games —
modeling simple gestures and
celebrating when the baby imitates.

Twelve to Eighteen Months —
The Social Toddler

Research on social development
between twelve and eighteen months finds:

Social milestones:
First words — emerging at
approximately twelve months —
enabling new forms of social communication.
Parallel play with peers —
playing alongside rather than with other children.
Showing empathy — distress
at others’ distress — attempting
to comfort upset others.
Beginning of pretend play —
simple make-believe — feeding
a doll, talking on a toy phone.
Strong preference for familiar
caregivers — and continued separation anxiety.
Beginning to understand social rules —
“no,” “mine,” “wait.”

What parents can do:
Provide opportunities for peer
interaction — even parallel play.
Respond warmly to empathic
behavior — “You gave [friend]
a hug because they were sad — that was so kind.”
Begin simple pretend play together.
Begin introducing simple social
rules — warmly and patiently.

Eighteen to Twenty-Four Months —
Social Skills Grow

Research on social development
between eighteen and twenty-four months finds:

Social milestones:
Vocabulary explosion — rapidly
expanding vocabulary enables
more sophisticated social communication.
Beginning cooperative play —
simple cooperation with a peer toward a shared goal.
Sharing — beginning to understand
and practice sharing — though
still very challenging.
Turn-taking — beginning to
understand and practice turn-taking.
More sophisticated pretend play —
sustained make-believe scenarios.
Expressing emotions verbally —
“I’m sad,” “I’m angry.”
Beginning to understand others’ emotions —
“Baby crying — baby sad.”

What parents can do:
Continue emotion coaching —
naming and validating emotions.
Support peer interaction and
beginning cooperation.
Model sharing and turn-taking —
genuinely and warmly.
Read books about emotions and social situations.

Twenty-Four to Thirty-Six Months —
Toward Genuine Social Competence

Research on social development
between two and three years finds
significant advances in social competence:

Social milestones:
Cooperative play — genuine
play with another child toward
a shared goal — emerges and develops.
Shared pretend play — creating
and sustaining shared fantasy
scenarios with peers.
Friendships — preferred specific
peers — begin to emerge.
More sophisticated understanding
of emotions — understanding
that emotions have causes and consequences.
Beginning theory of mind —
early understanding that others
have different thoughts and feelings.
Conflict — and beginning conflict resolution —
with adult support.
Understanding of fairness —
the beginnings of “that’s not fair!”
Gender awareness — beginning
to identify as a boy or girl
and to notice gender in others.

What parents can do:
Facilitate genuine peer play —
including unstructured playdates.
Support conflict resolution —
acknowledge both children’s feelings —
help generate solutions —
but allow children to practice
resolving conflicts themselves where possible.
Continue emotion coaching.
Begin perspective-taking conversations —
“How do you think [friend] felt?”
Read books with complex social
and emotional themes.

Signs That Social Development
May Need Support

Research on social development
and early identification supports
seeking professional assessment when:

At twelve months — no pointing,
no showing, no waving, no back-and-forth sharing of sounds or expressions.
At sixteen months — no single words.
At twenty-four months — no two-word phrases.
At any age — loss of previously
acquired social skills.
Significant difficulty with
peer interaction that is not
improving with experience and support.
Significant social anxiety
that is impairing daily functioning.

Try This This Week

Practice 1 — The Serve and Return Practice
What it is: A deliberate daily
practice of serve-and-return
interaction — the most important
single support for social brain development.

How to do it: This week — with
your infant or toddler — practice
genuine serve-and-return:

Notice what your child is
attending to — a sound, a face, an object.
Respond to their communication —
vocalization, gesture, expression.
Wait for their response —
and respond again.
Keep the exchange going —
back and forth — as long as the child is engaged.

Why it works: Research by
Shonkoff and colleagues consistently
finds that serve-and-return interaction —
the back-and-forth exchange
between caregiver and child —
literally builds the social
brain — establishing the neural
connections that social competence requires.

Practice 2 — The Emotion Naming Practice
What it is: A deliberate daily
practice of naming emotions —
building the emotional vocabulary
and awareness that social development requires.

How to do it: This week — throughout
the day — name emotions as they arise:

In your child: “I can see
you’re feeling frustrated.”
In yourself: “I’m feeling
a little tired right now.”
In books and stories: “How
do you think that character is feeling?”
In others: “That child looks sad —
I wonder what happened.”

Why it works: Research on
emotional vocabulary and social
development consistently finds
that children who have rich
emotional vocabularies — developed
through consistent emotion naming —
show significantly better social
competence, empathy, and conflict
resolution than those with limited emotional vocabulary.

Practice 3 — The Peer Play Facilitation
What it is: A deliberate weekly
facilitation of peer social experience —
the most important context for social skill development.

How to do it: Once each week —
provide a genuine peer social experience:

An unstructured playdate with
a peer of similar age.
A neighborhood play opportunity.
A toddler group or community playgroup.

Allow genuine interaction —
including conflict — with warm
adult presence but minimal direction.

Why it works: Research on
social development consistently
finds that genuine peer social
experience — particularly unstructured —
is the primary context for
social skill development in
early childhood. No amount
of adult instruction replicates
the genuine social practice
that peer interaction provides.

The Bottom Line

The social development milestones
of the first three years —
from the newborn’s social smile
to the three-year-old’s shared
pretend play and emerging friendships —
represent one of the most extraordinary
developmental journeys in human
experience. Research is clear:
consistent warm responsive caregiving
builds the secure attachment
that is the foundation of all
social development; serve-and-return
interaction builds the social
brain; emotion naming builds
emotional intelligence; and
genuine peer social experience —
facilitated but not directed —
is the primary context for
social skill development.

Sources

Bowlby, J. (1969).
Attachment and Loss: Vol. 1. Attachment.
Basic Books.

Shonkoff, J. P., & Phillips, D. A. (2000).
From Neurons to Neighborhoods.
National Academy Press.

Zahn-Waxler, C., et al. (1992).
Development of concern for others.
Developmental Psychology,
28(1), 126–136.

Meltzoff, A. N., & Moore, M. K. (1977).
Imitation of facial and manual
gestures by human neonates.
Science, 198(4312), 75–78.