An afternoon of fun.

Chalk paint is quite easy to make, and a blast to decorate the sidewalk and driveway with.

Measure and mix equal parts cornstarch and water in separate containers; stir well.
Add food coloring and stir more.
Paint rainbows, flowers, houses, bugs, butterflies, suns and a jumbo fish. Splatter dots everywhere. Or whatever speaks to you.
Let the rain wash it away. Repeat.