If they don't have the background, start with what they do have, and work from there. Don't insult them or try to intimidate them with your brilliance. Stick to what you know and get advice from teachers. This is less a problem at the elementary level - those kids haven't yet been socialized to fear what other students think of them. They may not know the specialized jargon, but they're smart.
Students cluster around the heaters.
They understand the difference between radiation and convection. If you 're doing the Solar System but only get out to Venus, that's okay. Amateur astronomy groups get lots of requests for volunteers for school visits. Success takes time, energy, commitment. The Deans understand, but it's the department that counts, and the acid test is how departments do their hiring and tenure.