Explain that symmetry means to be the same on both sides when folded at a certain point. You can show this with different shapes (circles, triangles, flowers, etc.).
Cut a butterfly shape by folding paper in half, tracing the shape, and then cutting it out.
Paint one half of the butterfly using the primary colors, being sure to clean the brush in between colors. In between each painting, ask them to fold the butterfly over and rub. Let them know it’s okay to mix colors on the butterfly.
Open the butterfly back up and keep painting on one side until the entire butterfly is painted (folding repeatedly). Remind them to move quickly between painting and folding.
When it is complete, ask them to point out an secondary colors that have developed.