I can't remember if I read about this particular idea on a post over at Play at Home Mom or if I'm taking several posts and combining them into one, but I know I came up with the general idea through reading about their outdoor play.
I basically used several glass and plastic containers that we had and filled each one with different amounts of water and food coloring.
I also had a few empty containers, a big bowl, and a spray bottle filled with water. Bea loves to pour and dump anything from one vessel to another so I knew this would be a big hit.
And not to be left out, here's a picture of Charlie enjoying the sun.