The National Museum of Natural History at the Smithsonian has had
a Discovery Room for almost 20 years, operating quite successfully. In
fact, some of the staff authored a book on starting Discovery Rooms.
MANY museums have emulated that one, or have initiated their own. I
don't know an E-Mail number for them, but you could write for more
information. NMNH, Smithsonian I., Constitution Ave., Wash. DC 20560.
Or FAX no. 202 786-2567.  Good Luck!