What is the inside of a child psychiatric hospital like?

Varies a lot. Most psychiatric hospitals for children try to be as "homey" as possible, with bedrooms and common areas. Most do have "quiet rooms" where children who are behaviorally out of control can be isolated and kept from harming self or others. Many have playgrounds and recreatoinal areas. Staff usually dress in "street clothes" rather than hospital garb.
Teamwork-based care. Most child and adolescent psychiatry units that i've worked on are caring environments that employ a multidisciplinary team including psychiatrists, psychologists, social workers, nurses, nursing aids, and teachers to address all aspects of a child's mental health. Usually the days are spent in therapeutic groups and school, and a comprehensive aftercare plan is created prior to discharge.