You didn't tell how old the small kids are. This probably matters. 7 year olds are different from 11 year olds are different from 15 year olds. Whatever you pick as the topic, you should probably come up with a treatment that simpler than what you'd think necessary. And then make it even more simple.
Basic rule of thumb is probably that kids will deal with the concrete a lot better than with abstraction. You might want to start with some regular science popularization about the concrete stuff out there, like the atomic structure of matter, orders of magnitude, stars and planets, animals and evolution. Reading through A Short History of Nearly Everything might give you ideas about this. Maybe proceed to how the scientific method works with hypotheses, experiments and falsification, while trying to keep things very grounded in concrete examples. Also, stuff by Carl Sagan might be good. He had science popularization, and I remember liking his critical thinking book The Demon-Haunted World when I was 15.
I remember taking a course about logic in the context of real-world problems in high school when I was 17, which was the basic Aristotelian binary stuff, and thinking that the stuff seemed ridiculously useless against any sort of real-world problem, both from the obvious problem of mapping simple binary predicates to real-world states of affairs and from the fact that it didn't look much like the way people seemed to be actually reasoning about things. Didn't have any idea about Bayesian reasoning back then. I probably would have been interested in learning about trying to tackle real-world stuff with probabilistic logics at 17, but then again, I also would have thought the Harry Potter books were crap with terrible worldbuilding.
So, basically, good luck, this looks like it might be a lot of work to do well. You're dealing with both the fact that these are kids and that they're not necessarily the sort of people already receptive to this sort of stuff who might end up hanging out at LW.
You didn't tell how old the small kids are. This probably matters. 7 year olds are different from 11 year olds are different from 15 year olds. Whatever you pick as the topic, you should probably come up with a treatment that simpler than what you'd think necessary. And then make it even more simple.
This is something I've struggled with (am still struggling with, really) in my time teaching kids as a volunteer. I already knew the basics of child psychology, remembered more or less what concepts I could expect kids to handle at various stages of developm...
At my local Harry Potter fanclub (Bogotá, Colombia) some members teach "classes" on subjects they're passionate about. We've had informal courses on history, creative writing, English, etc. But recently some other classes have appeared that have made me worry seriously: astrology, divination, ancient runes, and all other sorts of nonsense. They're not taught as folklorical pieces of the past, but as serious practices that are supposed to actually work. I think this is particularly dangerous for the small kids that comprise the majority of the fanclub and still need help learning that magic doesn't exist.
So I proposed the fanclub chief that I could teach a Muggle Studies class: logic, critical thinking, philosophy of science, etc. In two weeks we'll have our first class, and I intend to begin talking about the most common biases. I already downloaded this website's PDF guide to holding a Less Wrong meeting. Aside from that, what can you suggest for a successful Muggles Studies course?