Hiding is a behavior sometimes associated with an anxiety disorder and past or recurring trauma. Hiding is more than just exhibiting shyness. It is the ability to disappear in plain sight and in a group, even a small group in a small room. It is sometimes learned as a coping mechanism used to disappear in the face of trauma when escape is impossible or at the least extremely difficult.
It is not the same as learned helplessness where a person simply gives up and gives in. It is a purposeful coping mechanism.
This is not just the typical child playing hide and go seek or just hiding for fun. That is very typical behavior. This is the child who seems to be able to just disappear and be forgotten.
This MAY be a behavior to be concerned with and talk with your physician or a mental health professional about.