Choose a manageable set of concepts and theories to introduce to your students. Consult a textbook or online resource (see references, Econ Guru Economics Guide) to help determine which topics are best for your group. Your choices might include the history of economics, key theories, core concepts, and important economists.
Choose a text or several texts appropriate for younger students; if you cannot find such texts, adapt existing ones (see references, Basic Economics or Economy Watch). Use short excerpts from a number of sources rather than using the entirety of one source; a textbook, economics reader, or series of essays may be appropriate. Provide students with a glossary to help them make sense of the readings (see references, The Economist).
Introduce core concepts, theories, and thinkers by reviewing the assigned readings together. Draw charts, graphs, and diagrams in order to clarify any challenging ideas. Use role playing games -- for example, one student as a seller and one as a buyer -- in order to make concrete the abstract concepts that you're introducing.
Discuss, debate, and use examples. Engage your students by asking them basic questions about economics -- even young students should be able to form opinions about ideas such as buying, selling, and earning income. Ask students what they think is useful about the the ideas they've encountered and what's not.