My four year old daughter calls C3PO "The Golden Man", and Vader is called "The Big Meanie" (quite accurate really). Chewbacca is Chewmacca.
All the other characters she ignores except Yoda (she has a cuddly toy version of him). Mind you she has only ever managed to watch a few snippets of the OT.
I know there is footage of a young girl describing C3PO as "The Shiny guy" http://www.youtube.com/watch?v=EBM854BTGL0
Any other examples of alternate names for the characters?