It's called "Thaumatrope". You can explain to the kids that this is how animation works, or you can just call it a "magic trick". Spinning the thaumatrope is a good exercise for little hands. It helps to improve a eye-hand coordination.
Print out the template or make your own design and follow the directions below.
You will need:
-Glue or scotch tape.
1. Print out the template.
2. Cut out the circles. If your child is old enough to work with scissors, let her do that herself.
3. Align the circles back-to-back. Put it on the window or against the light to check that the butterflies are above the flower.
4. Glue the circles together.
6. Use a piece of scotch tape to secure the pencil.
7. Hold it between your palms. "Grind" your palms again each other. And watch the new [combined] image appear as the thaumatrope spins.
(images by Mamalya)