I would enjoy a "hall of infinities", listing countable ordinals... not all of them, but enough to get the idea across.  It's possible to draw nice pictures of some them, at least up to $\omega^3$ or so, and even kids know how to count, so they might enjoy knowing what comes after the numbers they learned about in school.

I tried to present this information in story form in ["week236"](http://math.ucr.edu/home/baez/week236.html) of _This Week's Finds_.

Actually, now that I think about it, there should be a "hall of numbers" that starts by listing lots of interesting natural numbers and then moves on to countable ordinals.

MIT has an "infinite corridor" that would do well for this, but I guess a shorter version would still be okay.