In the newest trailer, it appears that Luke is telling a family member about the Skywalker legacy, and how powerful it has been with the Force. And since Luke has no living relatives (Other than Leah) he MUST be talking to his son... Ben.
Now, it's debatable that since the timeline is about 20 years after Luke and Mara Jade marry (and have a son) that their entire relationship will be discussed, or shown in flashbacks... Perhaps Mara will have died in this version of events: but my money would be on two strongest possibilities:
1) Luke is talking to his son. Who will be the focus of the new movies, along with the 3 Solo children.
2) The child's mother will be Mara (since there is SO much source material to work with... And Star Wars fans love her character so much)