I think the big assumption that kids can't get "complicated" ideas is faulty. Sure, they lack rigor, and often will just get the sketch of the idea. And it's

I think the big assumption that kids can't get "complicated" ideas is faulty. Sure, they lack rigor, and often will just get the sketch of the idea. And it's a lot more work to think about how to put things in the terms that a kid will understand given their knowledge so far. But this idea? "Infinity plus one?!@" --- this is a conversation elementary school kids have on their own. Pulling it a little closer to a sane footing in ordinal analysis is not hard. Half of six year olds can handle it. On the other hand, there's not a lot of obvious utility to teaching a six year old this particular concept early. On the gripping hand, there is a cost to keeping kids in a bubble where you don't talk about any big ideas (of whatever sort-- mathematical, philosophical, historical, linguistic) at all, or excessively dilute them to the point where they're meaningless.