A project we (my great grandkids and I) found fun was to buy packages of clear plastic ornaments at our local Dollar Tree store and then drizzle (thinned with water) colored acrylic paints inside, swirl the paint around a little and then let them dry. Glitter, feathers, wiggly eyes, etc. can be glued on to further decorate them. They are so original and could be a fun project for your girls. Also, they might paint funny faces on rocks to use for paperweights. (Or if they are small and flat enough, glue magnets to the backs of them to use on refrigerators.)
Have fun!