Closely related to infants' emotional development is their social development; it's through relationships with caregivers and other people that children learn how to apply and use their emotions, expressions, and emotional understanding. During infancy, healthy social growth is mostly about creating attachments with caregivers. Babies in Erickson's trust versus mistrust stage (usually occurring between ages 0 to 12 months) will develop trust and love for their caregivers because they are given adequate love and nurturing from their environment or will develop mistrust and indifference for people and the world because they aren't given those resources. There are degrees of trust and mistrust, however. These degrees of attachment have been further refined in other theories, including most centrally, John Bowlby's Attachment Theory (Theory and John Bowlby)
According to Bowlby, there are four phases of attachment during infancy: preattachment phase, attachment-in-making phase, clear-cut attachment phase, and formations of reciprocal relationships phase.
In the preattachment phase, which spans from birth to about age 6 weeks, babies' automatic reflexes, and activities such as grasping, crying, and rooting, will cause caregivers to want to attach to babies. Caregivers will feel needed and want to meet all their babies' needs. However, at this time, babies are not yet attached to any one caregiver, and they do not care if they're held or cared for by strangers. However, some research suggests that babies know their mothers' voice and unique scent from birth and recognize their mother that way. During this phase, babies may sometimes respond to social interaction from caregivers; at other times, babies may not readily respond at all. Babies can smile automatically in response to voice and touch from birth to about age 2 months, which encourages caregivers to interact with them. This interaction will increase their mental, emotional, and social growth and learning.
During the attachment-in-making phase, which spans from about age 6 weeks to about 6 to 8 months, babies begin to react differently and more quickly to primary caregivers than strangers, and they start building trust in caregivers to fulfill needs. They are slowly starting to count on their caregivers to take care of them. However, infants at this stage are still not distressed at being separated from particular caregivers. During this stage, they continue to make gestures and actions that help encourage caregivers to bond with them. Babies begin making eye contact around age 2 months, and can smile intentionally between ages 3 to 5 months. They start reaching for familiar people and caregivers, as well.
Next, during the clear-cut attachment phase from about age 6 to 8 months to age 18 to 24 months, babies become solidly attached to their caregivers and separation anxiety emerges. Babies want to maintain contact with main caregivers and they will express their displeasure in ways such as clinging to Mom, following Grandma around to the door, or crying when Dad leaves. During this phase, babies are also beginning to develop social skills and interactions beyond just attachment. Babies can start playing simple social games like "Pat-a-Cake" around 9 to 11 months. They also like to participate in social rituals like saying hello and goodbye, and chiming in at social functions such as family dinnertime. Babies will also begin social referencing, looking for social cues from other peoples' emotional and physical reactions to new stimuli in order to know how they should respond. For example, they will watch how their caregivers react to hugs from friends or a knock on the door.
The final phase of attachment, the formation of reciprocal relationships, spans from about age 18 months to 24 months and beyond, is a time when babies start negotiating with caregivers to meet their needs and to keep them feeling safe and attached. They'll express their needs and desires in order to keep feeling satisfied. Also during this time, babies start to understand "no" and other boundaries that make certain objects and activities off-limits. They may try to "cover up" when caught doing something wrong in order not to get in trouble. Social interactions continue to mature as they observe family routines and start to participate in them. They also begin "to and fro" play with caregivers and other peers. While this isn't quite interactive play yet, they start realizing they can include other people in their fun and play.
Environmental and personal complications can impede social and emotional development. For example, symptoms of pervasive developmental disorders such as autism or Asperger's may be first noticed during this time. While the causes of these diseases have not been found to date, the symptoms have been identified and best-practice treatments have been defined. Children with pervasive developmental disorders experience a wide range of difficulties, including problems relating to others. They are often unable to or have extreme difficulty interpreting other people's feelings or language and understanding how people relate, interact, and communicate in society. In infancy, this sort of problem often first manifests as a child who does not mimic parents' behavior and communication normally despite having normal sensory abilities such as hearing and vision. Caregivers should consult their pediatrician if they suspect their child may have a developmental disorder.
Other environmental conditions can affect babies' social and emotional development as well. As stated earlier, infants and young children need consistent interaction and provision of basic needs and nurturing in order to develop well and robustly. Children who are deprived of consistent love and affection, from consistent caregivers, may not develop the ability to bond properly, both socially and emotionally. Children who grow up in orphanages or who spend their early years in different foster homes probably will not have the opportunity to bond to a caregiver who will meet their emotional needs. Even if these children are adopted into a loving family in middle childhood, they may have difficulties learning to trust, bond, and show affection and empathy toward that family. Nevertheless, children with the most bleak and traumatic early years are sometimes able to heal and slowly develop those emotional regulation and attachment abilities when provided with long-term, consistent, and intense nurturing.