Here is the post allegedly from the mother of Lily Gaubert who is incorrectly identified as Allison Wyatt.
http://instagram.com/p/TS1VEhSC_U/
If you cursor over the photo, the post from the mother appears.

I find no MSM correction, and even more odd, I find no parent of Allison objecting to having the wrong photo posted of their daughter.

Here is a neighbor grieving the loss a week later. It seems like she would have noticed by then that the little girl in the photos was not Allison, and that the little girl next door was not dead.
http://www.ctpost.com/news/article/Allison-Wyatt-liked-to-ga...

I don't know if any of these claims are legit, but it seems like if this was a hoax someone would have debunked it by now. Maybe someone here can get to the bottom of this?