Liquid dish detergent
Pour a small amount of liquid dish detergent into each paper cup (children can share cups). Pour milk into each pie pan. You only need to pour enough milk in the pan to cover the bottom
When the group is ready, drop one drop each of 4 colors of food coloring around the edge of the pan. The milk does not change color if we keep the pan still. Children add one drop of liquid dish detergent into the middle of the pan with a medicine dropper. The colors will swirl! After they watch the colors swirl for a bit, give them a toothpick to dip in the soap, then dip in the pan repeatedly to make the colors swirl some more. Instruct children to dip their toothpick into the milk, but not stir.