choccyJules said on the old thread: I don't get it either, Aitch, cos Amy writing in the afterword of the book, is telling him to (paraphrasing) 'go to Amelia and tell her to be patient as she'll have fab adventures one day'. If he goes, well, he's there isn't he, so she'll stop waiting in the cold garden (or back in the house if she's sensible)...but of course he won't travel with her yet as she's a child SO when he turns up yet again and Amy's now a grown-up strippergram how come she gets so cross with him for not coming back in the inetervening years. If he's now (due to reading the book) going to do just that?
Sorry for the long quote, it's just so I don't have to keep popping back to the old thread to see what you said...
OK, the Amelia he is now going back to see (and the Amelia we saw in that clip two years ago) is the post-crack-mending Amelia. We don't know what she did when the Doctor came back.
But I would think that once the crack had been removed from Amelia's wall, she grew up with her parents, as normal, except that she had still met the Doctor when the TARDIS crashed in her garden, that he had promised her a ride, went to the moon and didn't come back. So she still grew up with an obsession about the raggedy doctor, biting psychologists and hoping he would come back. I think Amy asked the Doctor to go back to her younger self sitting waiting in the garden and tell her that he would come back to pick her up when she was older and she would do all those things, so that instead of thinking he'd forgotten about her and getting obsessed, she would just have faith that he would come back. So she would have a happier childhood.
Just don't ask me why Amelia's parents didn't notice the TARDIS crashing in their back garden. Perhaps they were just heavy sleepers....