Vader didn't know that Luke existed. He was able to detect he was strong in the Force, but if you think your unborn child died with its mother 19 years prior, the idea that the pilot trying to blow up your space station and then be a pain in your Dark Side for the next few years is your son is the furthest thing from your mind.
If Rey was the daughter of Leia or Luke, and they sent her away, and she came back years later, showing a talent for the Force and being about the correct age of the daughter you sent away all that time ago, I feel like they'd at least ask the question of where she grew up.
"Hey, you're not from Jakku, are you?"
"I am actually."
"Welcome home! I'm your long lost mom/dad! Here's your Uncle Luke/Han. You should probably do something about your brother/cousin, Ben."