I have a feeling that pretty soon I'm gonna run out of answers.
A couple of days ago, Sebastian and I were reading a book about Mars. He kept stopping me to ask questions like, "How did they originally figure out that the earth was rotating around the sun?" In the course of that conversation, he also made his own mental leap to figure out that we have time zones because the earth spins on its axis.
Just now, Dante called me up to his bedroom so he could ask me this one: "You know how people are always talking about time as the fourth dimension? Does that mean fourth dimension in relation to the three dimensions of height, width and depth?" This was after a dinner conversation in which he pondered how gravity affects time, and tried to figure out if time is different on Jupiter, and if so, if it's enough of a difference to be perceptible.
I know that everyone thinks their kids are amazing, but my kids really are amazing!