Selective mutism is a condition which deprives some children of the ability to speak at will. For the youngsters affected - and their parents - it can cause great anxiety, lead to isolation and hinder a child's progress. For the first time, cameras have been allowed access to one of the only intensive-therapy summer camps for young people with selective mutism. Over the course of a week in New York City, Our World hears from parents and children about living with the condition.