"Why there's no sun?"

He asks "why there's no sun" almost every night. And, "Where the sun go?" And, "Why it's night time?" During the day he asks, "Why it's day time?" I tell him the same thing every time: This happens every day, the sun comes up and it's day time. Then the sun goes down and it's night time. That's when the moon comes out. Tonight on the way home he asked me over and over and we had a long conversation about it. He was also asking. "I want chicken and fries because I'm hungry". I laughed and said, "I know you ate, you're going straight to bed!" Then he cried. Clearly he was very tired.