Pretty decent as a stand-alone one-shot. However, given where you leave things, it seems... cut off. For example, the ending ("What have I gotten into?") seems to be leading into another chapter, or at least setting up for something. So, given that the story basically seems to be set up for chapters and not as a one-shot, a few suggestions to think about/explore/expand upon if you want:
-Who is this story focusing on? Harry? Rebecca? Rose? Harry's kids? all of the above?
-When is this set? 1 year after Hogwarts graduation? 5 years? etc.
-Who's still around in terms of leadership? Fudge? Scrimegour(or however you spell his name)? Dumbledore? Do they get along with Harry and Co.?
-How did the war go for Harry and Company?
-How did the wizarding world fare during the war? Is everything still being rebuilt 10 years later? Did they fix it all the next day? Somewhere in between?
-How does the public see Harry? Do they worship him? Hate him for not ending it earlier? Are they apathetic and don't care anymore now that Voldemort is dead?
-Which of Harry's friends and classmates are still around? Remus? Tonks? Ron? Ginny? Neville? etc. If they're around, what are they up to? If not, what happened to them (& when did it happen)?
-I'd suggest staying away from any sort of ministry forced-marriage law plot device, as it seems like it'd contradict Hermione's comments.
-Will you re-introduce Dudley later on as an antagonist? or will he have some sort of miraculous change of heart? What about Petunia? Vernon?
-How old is Rose? About to start Hogwarts? 5 years old?
-How big is Harry's Family? What does Harry do for a living? What do their titles (Lord/Lady) imply? Is it ceremonial or is there more to it?
-How skewed is the population problem? Is the polygamy solution just something Harry and his friends are doing, or is it something that pretty much everyone is doing?
-Most importantly, What is Harry's reaction to this news?
As I said long ago at the beginning of this review, it is a pretty decent one-shot. However, it would be much improved if it was either extended into a multi-chapter story, or if it was extended/edited so the last paragraph wasn't so open-ended.
p.s. err, not to poke any gaping holes in your plot, but... to the best of my knowledge, the Dursleys have never been to the Leaky Cauldron. Well, maybe Petunia has been there, but certainly not Dudley. How does he immediately recognize it?