It is hard to imagine that there are people out there that don't know that Vader is Luke's father, but it's more likely than you think.
J just got back from my nieces 16th bday party awhile back and I asked my nephew everything he knew about Star Wars. He's heard of Darth Vader and Luke Skywalker and Yoda (or "the little guy") but that's about it, he doesn't really know much about it other than those characters and the overall setting.... which is perfect
