Scarcity of resources is a fundamental economics concepts that kids need to understand. You'll use a large bag of popcorn to demonstrate this concept. Have the class come up row-by-row to fill their snack bags with popcorn. By the last few rows, the popcorn will be gone, and some of the class will have to go without. Unfair! Not unfair, just a perfect introduction to the reality of economic scarcity. After the demonstration you can discuss scarcity of natural resources and capital goods.