The Ending explained by Fulci himself.

"(...) to me the most tragic thing in The House Near the Cemetery is not the people who die, but that little girl who opens for her young friend the gates to the world of the Dead, and saves him from normality (i.e., from the monster who killed the boy's parents), but also plunges him into the Beyond. In fact, those children do not actually die: they just live in another world in which adults have no power. Finally, the most frightening thing is that the house stays there and will receive other visitors".

-- "The following interview was laboriously typed in word by word, by me, Lou Rinaldi, on Wednesday, August 27th, 1997. It was taken from issue 48 of Starburst magazine (an early 80's British publication) Volume 4, Number 12, August 1982 (publisher: Stan Lee). It was Starburst's "Zombies of the Screen" Special Issue. I have typed it in "as is," meaning there will be some confusing parts (for instance, the Starburst preface mentions a second interview, which is seemingly nowhere to be found). Oh well, enjoy!"

http://www.shockingimages.com/fulci/interview2.html

--Case solved.