And here's another good question.
How could the Doctor go back and visit young Amy from "The Eleventh Hour" when the timeline those scenes took place in doesn't exist any more. There never was an Amelia sitting on her suitcase in her garden once she got her parents back. That was kind of the whole point of the end of "The Pandorica Opens".
Anyone remember who wrote that episode?
Wasn't it said that the Pandorica contained the universe "as it was
" inside it? So the gambit in that episode relied on there being enough of the original universe, that still exists in the Pandorica, to completely restore said original universe as it was, albeit with Amy "remembering" her parents back into reality at the same time.
The events in the first episode must have happened otherwise why would Amelia's mother mention that they sent her to countless psychiatrists about her obsession with the "Raggedy Doctor", if the Doctor had never visited her in the first place to become obsessed with?