Obi-Wan having a family or children is an interesting prospect. Some of the EU had him close with another padawan. And we also saw the storyline between him and Satine in Clone Wars. So there's some potential backstory there to show that Obi-Wan may have strayed from the monastic life of the Jedi.
Another angle? Obi-Wan was witness to Order 66, and knew that the Empire was hunting down the Jedi. He was also aware of Anakin and Padme's relationship and that their children could be that potential new hope for the Jedi, or perhaps a new apprentice for the Sith. With that in mind Obi-Wan may have wanted to make sure that a Force sensitive child might carry on his own legacy.
So if Obi-Wan does have a kid and she is force sensitive, what's with the dialogue between Obi and Yoda in Empire basically stating Luke or another (Leia) are their only hope? I'd think mini-Obi might have factored into that conversation. I just don't see the need to tread down that pre-original-trilogy path.