vote_for_palpatine said:
"There is some of that already with the Naboo celebration being the Emperor's theme up tempo and sung by children..." I have read this idea before, on other SW sites. I don't hear it at all. I've listened as closely as I can to make sure I wasn't the odd man out, and my conclusion stands: one is not an arrangement of the other. They are two different pieces.

Try whistling it. That's how I realized it, trying to whistle the "Happy Naboo Children Song" and realizing it's the same melody as the Empy's Theme.