A dinosaur dig is a popular, out-of-the-ordinary and fun activity for children's parties. It is also a fairly inexpensive one, which will occupy the children for hours. With some plaster of Paris and bones from the butcher, you can create authentic-looking fossils. Then with a few props like garden trowels and whisk brooms, you can give the partygoers a fairly genuine paleontologist's experience.
Mix plaster of Paris according to manufacturer's directions (typically one cup of water to one cup of plaster). Use a quarter cup of coffee or cola with every three-quarter cups of water; this will give the fossils an antiqued look, versus the stark white of plaster of Paris.
Create a dinosaur footprint. Some of the most remarkable finds are not fossils but footprints (including ones found in Colorado's Dinosaur National Monument). Mix and spread plaster of Paris in a thick oval on a baking tray. Wearing rubber gloves, use your hands and a trowel to create a large, three-toed three-clawed footprint, of the kind that a tyrannosaur would leave. Dust the drying footprint with loose earth or sand. Bake it as per manufacturer's instructions (typically 93.3 degrees Celsius for an hour or more).
Create a fossil bird or small dinosaur with chicken bones on a patch of plaster. Fossil birds are usually found embedded in rock, not as loose bones. Spread the plaster as above, then, press the bones into the plaster in a fairly good (but flattened) representation of the bird's shape. For an extra effect, press feathers into the surrounding plaster to create an impression, then remove the feathers. Dust the drying fossil with loose earth or sand, and bake as per manufacturer's instructions.
Splatter a large cow bone or something like it with plaster of Paris; then dust the plaster with earth, while it is still damp. The partygoers will use their trowels and water to remove the earth to reveal a clean fossil.
Fashion dinosaur teeth out of plaster. These are typically conical and fang shaped, slightly curved and broken off at the base. You may create your teeth and stand them up on, for example, a baking tray. Do not dust with earth or sand, as you did the other fossils. Bake as usual, and when they are cool and dry, spray the fossils with lacquer when they are cool and dry, for that smooth fossil look. Bury the teeth near your other fossils.
Guide the party goers to the area of the dig, armed with their trowels and whisk brooms. Give them an idea of what they will find---footprints, baby raptors, archaeopteryx, tyrannosaur teeth and so on. Stake off the area with the tent spikes and twine, creating an authentic paleontologist's grid of perhaps one-foot-by-one-foot squares; then assign a square to each child (making sure each square has something to find). Have them begin their digs with the trowels, then clean away the earth with their whisk brooms.
Provide buckets of water for the children to clean off the butcher bones. Do not use water on the footprints, chicken bones or teeth; this will soften and ruin the plaster.
Plaster of Paris takes hours, sometimes days to dry; make your fossils early in the week for a weekend party. Do not bury the fossils until the day before or the day of the party. Any moisture will soften the plaster. Most parents opt to stage their digs in a sandbox, which makes for easier digging and confines to dig to a safe area. Do not bury the fossils more than two inches deep, as children will become quickly bored.