At dinner last night:

DS4: See mama? I made a pattern. (He describes the pattern of food.) It goes around and around. Just like the water cycle!

Me: Yes! Water rains down from the clouds, goes into streams, then rivers, then the oceans, then back into clouds. Around and around.

DS4: You mean it evaporates, mama. It doesn't just go back into the clouds. It evaporates.

Me: Yes, yes it does. Of course.