One of the questions he has asked a few times is why the sun goes down. He's known for a while now that the Earth spins around in space, and that when it's daytime here, it's night time on the other side of the planet. A couple of days ago he asked again, so I squatted down and told him again about how the Earth rotates, and I spun around, telling him to pretend he was the Sun and I was the Earth, and as I spin around, he's looking at a different part of my body, kind of like how the Sun shines on a different part of the Earth as the planet spins.
Before I could try to explain to him the reason, though, someone else mentioned that the Sun goes down because it gets tired and goes to bed. Maybe it's just me, but this is such a boring answer. I was talking to my wife about the subject earlier...the thought that the Sun just goes to bed at night and wakes up in the morning does nothing for me. Maybe it's because I'm not a toddler or whatever, but the thought of the Earth spinning through space, while a star shines down on different parts of the surface...it's just fascinating to me. Maybe I'm cheating my kids out of an imagination by telling them the truth about things, I dunno. I wonder if when they are older, they will find the facts as fascinating as I do, or if they will feel bad about not hearing the stories.
*I do admit to telling him that flue-gas stacks on the horizon while we drive were cloud factories once.