Rumours and theories of a Skywalker sprog have abounded ever since Episode VII was first announced, although it is most commonly thought that it'll be a child of Han and Leia in the film. However, there is still a belief (and a slim possibility) that Luke has a child now. The most obvious choices here are Rey and Kylo Ren (another widely-held theory has them as brother and sister). That would fit with Kylo Ren being Force sensitive, while there's an excellent chance it'll be Rey, not Finn, who has the powers out of those two. Domhnall Gleeson was also rumoured to be playing Skywalker's son, which would mean that his offspring is now working for the forces of evil as a general (or is actually a double-agent type of character who's not really working for the First Order at all). As for a final possibility, who's the other main character we haven't seen much of in the marketing? One who's been shown piloting an X-Wing with the same skill as Luke? Poe Skywalker, anyone?