We poured water into cute little ice molds (from IKEA) and put a drop of food coloring in each one. We observed the food coloring diffuse through the clear water.
When the water was frozen into its solid state, we headed outside. Each girl had a waterbottle with a squirt top.
Heads up...this was messier than I thought it would be. The food coloring did get on the girls' gloves and coats(they're in the wash now). Also, the girls couldn't hold the tiny cubes well with their thick gloves and ended up taking them off...which made for cold fingers. The outcome was pretty though!