Use an apple to demonstrate the layers of the Earth. Take enough apples to class for each student to have a half of one. As you discuss the layers of the Earth, slice and distribute apples. Draw an apple on the board, adding seeds, marks near them to represent the core, and shade the outer area to represent a peel. Point out that the apple also has a core (seed area), mantel (apple flesh) and crust (peel).
Provide students with candy-coated, chocolate covered peanuts. Have students bite the candy in half and explain that the peanut is the core, the chocolate is the mantel, and the coating is the crust. If time permits, you can make a more complex edible model of the Earth's layers using a cinnamon candy disk for the core, ice cream for the mantel, and crunchy graham cracker crumbs or quick-hardening ice cream topping to represent the crust.
Provide clay for each student and instruct them to mold the layers of the Earth as you discuss them. After giving students a chance to mold the layers into a ball, provide them all plastic knives in order to slice the clay earth open. Refer to the clay models often as you discuss the layers of the Earth. For very young students, provide pre-cut circles and glue sticks to create a paper version of the Earth.
Use a small and large foam ball to make a foam model of the Earth's layers. Cut both in half and hollow the center out of the large ball in order to inset the smaller one. Paint the core if possible. Set the core into the middle of the large ball (the mantel). Wrap the outside of the entire cross-section with duct tape. The duct tape represents the crust. Note the thickness of the crust.