Make the paint:
1/4 c. cornstarch
1/4 c. water
a few drops of food coloring or washable tempera
Mix each color in a small container.
Grab some paintbrushes, some sponge shapes, and any other mark makers and head outside.
The sponges were the biggest hit. I need to get some more of those magic grow capsule sponge shapes because they would be great stamps!