A prism

Take a prism and go outdoor to show the experiment to the kindergarten kids.

Place the prism in sunlight, so that the sun light rays fall on one side of the prism.

Make the children observe the vibgyor (Violer, Indigo, Blue, Green, Yellow, Orange and Red) of sunlight.

This is because the sunlight is the composition of the seven light.

The prism refracts the sunlight and show it as different colours.