Kaleidoscope is a device, typically cylindrical or triangular in shape, consisting of three or more mirrors. We put small colorful objects, such as beads and pieces of glass in the instrument. The light enters from one end and the viewers look through the other end. These mirrors act as reflectors and provide multiple line of symmetry to the patterns due to repeated reflections in the mirror.

Source: http://byjus.com/maths/reflection-and-symmetry/