This phrase is a metaphor "The earth is the cup of the sun, That filleth at morning" it is stating that the Earth is like a cup that in the morning will be filled by sunlight.
irony is because the readers would assume that the kid would be scared and the kidnappers would be okay with what they're doing. it was the opposite. the kid didn't want to go back home, and the kid nappers were annoyed with the kid.
