This is a super simple science experiment with very few materials.
two paper towels or thin cloth napkins
3 similar glasses
2 colors of food dye
1. First fill with equal amounts of water into 2 of the glasses.
2. Add different colors of dye to each of those glasses
3. Arrange the glasses (as above) with the 2 liquid filled glasses on the sides of the empty glass.
4. Fold up each paper towel or napkin to make kind of a string to join each liquid filled glass to the empty glass.
5. Watch what happens.
Up to the picture above this project went fairly quickly. Well, within a few minutes at least. This is where the girls and I kind of lost interest and wandered off. A few hours later (when I went back into the kitchen to make dinner), I noticed all the water levels were equal.