A Wooly, wooly fun activity

Looking for an activity to get your kids thinking this summer? Our friends at the Mammoth Site sent us an idea for all of the young fossil hunters out there. We gave their activity a try and we had so much fun creating our own fossil casts. We’d recommend this activity for kids 4 and up, but little brother or sister might love watching and helping pick out toys to use to make fossils.

Create Your Own Fossils Casts

This hands-on activity teaches kids how to make their own replica fossils. Paleontologists make replicas of fossils, or casts, to make it easier to display and study fossils without the risk of breaking them.

Please be sure to read all directions before attempting the activity.  

What You’ll Need

  • Clay 
  • Plaster of Paris (This can be bought at most hardware stores) 
  • Objects to make molds of 
    • In keeping with the fossil theme, we recommend small plastic dinosaurs. You can make molds of these, or cast their footprints and make a trackway! 
  • Lotion 
    • This helps the clay to not stick to the object you are casting  
  • Disposable plastic or paper cup/bowl 
  • Popsicle stick 


  • Warm up your clay by rolling it in your hands. This will help your fossil make a better impression.  Your clay is ready to go if you can press your thumb into it and see your thumbprint. 
  • Flatten your clay on the table. You want your clay to be about ¼ inch thick to prevent the clay from getting a hole in it 
  • Flip your clay over. This gives us a flat surface to work with
  • Make your impressions! This can be done by pressing toy animals into the clay or by making a trackway of animal footprints. You can even make an impression of your own fingerprint! You may decide to make a couple of different impressions before you decide which one to cast. To reset your clay, repeat steps 1-3.  
  • Once you have an idea of what you want to make a cast of, reset your clay so that you have a fresh surface to work with. If you are casting a toy dinosaur or animal, cover the surface of the toy with a very thin layer of lotion. This acts as a mold release so your impression won’t be ruined by removing the object.  
  • Gently remove your object by gently peeling it from the clay
  • Next step is to mix your plaster.  Choose an area where you can mix your plaster safely. We recommend outside so that you don’t get it on any difficult to clean surfaces in the house.  
    • Mix one part plaster to one part water in a disposable plastic cup. Cold water will give you more time to work with the plaster before it starts to set up.  
    • Stir your plaster and water mix with a popsicle stick. You want to make sure that there are no clumps of plaster before you pour. 
    • You know your plaster is ready when the popsicle stick can stand up in the middle of the cup without falling over immediately.  
  • Add your plaster to your mold. You want to over fill your mold a little bit. It can help to have multiple molds at once so that you use up all your plaster. DO NOT put plaster down the drain. To dispose of plaster, wait for it to harden and then throw it in the trash.  
  • Wait 1 hour or until the plaster has solidified in the mold. Plaster usually sets up in 1 hour, but takes up to 48 hours to fully cure. 
  • Gently peel away the clay from your mold and you should have a cast of the object you pressed into the clay!

If you and your kids enjoyed creating fossil casts, make sure to take a crack at excavating your own fossils with another prehistoric activity from the Mammoth Site.