I based this story on the idea that Amy's tombstone was recent in 2012, and that she was 31 when she was sent back in time. That would mean they landed in 1956. I also based it on the idea that the Silence erase memories, regeneration can cause amnesia, and that a child traumatized by the Silence and regenerating back into a toddler, may result in amnesia. Most people don't remember their life as a toddler.
This story takes place four years later. The year the Polaroid camera went national, 1973. When that toddler would have had four years to become secure in her home life. And Amy and Rory would finally have understood why the Doctor could never return for them. Because to do so would mess up River's timeline. Not because of the Timelock on New York.
(I also figure, Melody, 30 years later, may have had an accident that caused her to regenerate into the 10 year old Mels. And either Amy and Rory, old now, took her to Leadworth. Or maybe the Silence finally caught up with her again and forced her to regenerate into Mels, making her forget her previous life with her parents.)
Either way, I figure Amy and Rory got to raise their daughter. And that even if things didn't turn out perfect, they died knowing they turned out okay. Because they got to raise their daughter, and she still got to grow up beside them and become River and love the Doctor.
And, yeah, I think River likes Christmas.