We buried dinosaur bones in the sand box. They are actually cow femur bones. To clean them you can boil and then simmer them for around 24 hours on each side in apple cider vinegar. Just to warn you the smell is AWFUL! and it seeps into everything my house will never be the same. Some butchers have a machine that will completely clean it for you ask around.
Fizzy Bubbling Dinosaur Slime
Dinosaur Bone Excavation Sensory Bag
Dinosaur Bone Excavation Preschool
Dinosaur Excavation Sensory Table