One thing that we know about the human brain and brain development is that our knowledge of the human brain is only in its infancy. In-spite of this, we have learning incredible things about the brain and brain development over the past 20 years; however our knowledge is still barely in its infancy.
During the first three years of life a typical healthy brain in a typical healthy environment has been estimated to create as many as three billion synaptic connections per second. At around age three the process slows down significantly; though we continue to learn and synaptic connections continue to be made. At about age ten, the typical brain will begin to purge (prune) unused connections. This is sort-of like cleaning out and organizing your bedroom, removing what is not or least important and making everything left easier to find. Some times the brain does not perform this function very well, creating an ever increasingly cluttered and disorganized mind where it is difficult to find and access information. Fortunately most of us are able to continue to learn and discard useless information and connections through most if not all of our lives.
These first few years of life are extremely important to our development in many areas including attachment, and relationships, and language.
Attachment is one of the most fundamental protective factors which can be developed by children. With secure initial and ongoing attachment, many types of trauma and other difficulties experienced by children and adults are minimized. (This is discussed in more detail under Resilience.)
Attachment is one of the ways we learn to care for each other. When healthy from the aspect of both the child, parent, and others, it can bring great comfort, joy, and security.
There are many aspects of attachment, attachment disorder, and what is sometimes called detachment disorder. Instead of rewriting what others have written better, I'll just direct you to the supplemental material linked below. Please feel free to use the Google Scholar and/or Google Parenting Search engine below.
Reactive Attachment Disorder
Attachment Disorders: Insecure Attachment and Reactive Attachment Disorder
Attachment research in eating disorders
Disorganised-disoriented insecure attachment, a pattern common in infants abused in the first 2 years of life, is psychologically manifest as an inability to generate a coherent strategy for coping with relational stress.
Attachment Disorder Behavior Following Early Severe Deprivation
Attachment disorders: Assessment strategies and treatment approaches - Attachment & Human Development
Child Abuse & Neglect, Reactive Attachment Disorder: eMedicine Pediatrics: Developmental and Behavioral