Secure attachment is classified by children who show some distress when their caregiver leaves but are able to compose themselves quickly when the caregiver returns.[1] Children with secure attachment feel protected by their caregivers, and they know that they can depend on them to return. John Bowlby and Mary Ainsworth developed a theory known as attachment theory after inadvertently studying children who were patients in a hospital at which they were working. Attachment theory explains how the parent-child relationship emerges and provides influence on subsequent behaviors and relationships. Stemming from this theory, there are four main types of attachment: secure attachment, ambivalent attachment, avoidant attachment and disorganized attachment.[2]