Well, they've started to come back! I've had some months off, and my first visiting school group of the school year came by...
It was a 5th grade group. They were a little excitable, but not too bad, and mostly appropriate.
I started by talking about the moon. It's a good way to get the lights down quick, with a picture of a big moon up there, eyes can adjust to the dark a little more easily.
The teacher mentioned that they were talking about meteors. The moon is a good way to segue into that. I talk about the moon's craters, and how they are caused by asteroids flying in and smacking up the surface.
I then ask them, "Well, if the moon is being beat up by rocks, and is our closest next-door neighbor in space, is that something we should be worried about here on Earth?"
"NO!" they yelled back, which is what I expected.
"Well, we do need to worry about BIG asteroids. But really, most asteroids that head towards the Earth, we don't need to worry about, because we have a protection around the Earth that The Moon really doesn't have. What is it...?"
Usually 5th graders know it's the atmosphere. And this was a smart group. But it just got quiet for a second, until one brave soul ventured: "...Life Insurance??"