''Hidden Treasure'' is a follow up to Oaklander's first book, ''Windows To Our Children''. Most of the books available in working with this population are written from a traditional 'play therapy' point of view. The Gestalt Therapy-based approach provides a more effective method for psychotherapeutic work with children of all ages. The focus is on the relationship between the therapist and client, rather than observation and interpretation. It is a vigorous, dynamic approach.