Here's my theory.
Rey is Han and Leia's daughter, and here's how it could all make sense.
Kylo KNOWS Rey. After Kylo "turns" to the dark side, he goes and slaughters Luke's academy, where Rey is also being trained. He see's Rey at the young age of 5, decides not to kill her, because it's his own family, because he isn't fully committed. He captures Rey, wipes her mind, and leaves her on Jakku. Leia, Han, & Luke think she died in the slaughter. That's why they don't suspect Rey of being their daughter. However, throughout the film, she finishes Hans sentences, Han gives her those "looks" of "i know you...", stuff like that.
That's just my theory.