Ingredients: dish soap, milk, food coloring
If you google those three ingredients and add the words "science experiment" you will find a ton of videos. According to the internet, the results are better with "fat full" milk, but we had 2% and it worked well enough. Both girls really enjoyed it and we completed the experiment over and over again.
I am sure we will do this again since the items needed are household staples and once we figured out how to get the food coloring/milk "really moving" it became more exciting. The pictures don't do it justice. Super fun.