Provide preschoolers with a replica fossil dig so they can feel what it is like to "discover" fossils in the ground. To create a fossil dig, fill a cardboard box with soil, sand and clay, and mix them together well. Place shells and clean chicken bones inside the soil mixture. Press down on the soil mixture to compact it slightly. Allow the children to use shovels and paintbrushes to uncover the fossils from the box.
When paleontologists discover fossilized footprints from dinosaurs that they can't move from the location, they make a casting to preserve the image in plaster. Re-create this with preschoolers by pressing objects into soil, then pouring plaster of Paris onto the imprint. After the plaster sets, you can pull the casting off the soil and wash it off. Preschoolers can paint or decorate their castings with acrylic paint or markers.
One of the most exciting fossils to find are dinosaur bones, which can be replicated by preschoolers using paper mache, newspaper, tape and a cardboard tube. Bunch up newspaper into four separate balls. Tape two balls per end of the paper tube; this makes the structure look like a bone.
Create paper mache by combining 2 cups of flour with 1 cup of water in a pot, then heating it until it bubbles. Once cool, dip strips of newspaper into the mixture and spread it onto the bone. After you have added four to five layers of paper mache, allow it to dry completely. Once dry, paint the bone white.