Just add a few drops of food coloring to water in clear containers. I gave my kids a couple different kinds of medicine droppers to play with and they had fun for a long time mixing and adding colors.
Ezzy poured the water in containers.
Then he added a few drops of food coloring to each one.
Begin mixing with droppers. Kai played too.
But this activity really captivated Ezzy's (almost 5) attention the longest.