Requires transparencies.
Works great and kids love it; at the same time, serves to easily illustrate optical principles: join together 12 transparencies, and paste them at the four sides (about 5-6 cm of tape at the center should be fine. No need to tape the whole length of each side; plus it might lessen the flexibilty).
Now bend the "mirror" in any desired direction. If the lighting is reasonable, this works great (if not, add another one or two transparencies).
Did your kids like it? :-)