Use two mirror strips about fifteen centimeters long and three centimeters wide (you can go to the glass store to buy leftovers). Cut another piece of cardboard the same size as the mirror strip and paint one side of it black. Assemble the two mirror strips and a piece of cardboard as shown in the picture (the black side of the cardboard should be facing inward), tape them together, and secure them with two rubber bands. This becomes a simple kaleidoscope.

Put some colored confetti, colored glass beads, on a piece of white paper. Look at them through a kaleidoscope and you'll see many star-shaped patterns. Rotate the kaleidoscope and the pattern changes.
If you don't have a mirror strip, you can use a glass strip instead, but you should blacken or stick black paper on the glass side, with the blackened side facing out. But the kaleidoscope made of mirror strips looks much brighter than the glass strips.