Generally speaking, is it possible to volunteer in psychiatric hospitals?

I'm looking for some kind of volunteer work to do over the summer, and as I'm well-acquainted with the mental health field, I was wondering what most hospitals' policies are on volunteers in psychiatric wards. I'm particularly interested in pediatric psychiatry. I understand there is the issue of the privacy of patients (as well as my own safety), so I can anticipate most hospitals saying no. That being said, I know someone who volunteered in a forensic psychiatric hospital, so it must not be impossible. Is it worth a shot asking? If it counts, I know a highly regarded neuropsychologist in the area quite well who would undoubtedly put in a good word for me.