It's been raining for days and days and though I considered building an ark today, I opted instead to pull out some tried and true art activities.
Mix 2 cups of water and a little food coloring with 6 cups of cornstarch to create a nice, thick slime. Run your fingers through and make patterns in it. --from Natural Childhood
Later, we made tissue paper mosaics. This was my favorite activity a million years ago when I taught preschool during college. I loved to sit at the table with the three-year-olds and use diluted liquid starch to glue shapes of tissue paper onto white paper. That's really all there is to it. Just show the children that you can place the dry tissue paper on the white paper and then "paint" the water/starch mixture over the top.
Detailed directions for the tissue paper activity and some science connections are in Science Arts: Discovering Science Through Art Experiences.