I think it's really easy to miss the point of this "horror" film. Keep an open mind to the end and look for the clues.
For me, the Babadook was a manifestation of the mother's grief. The ending feels really awkward unless you think about how people deal with grief. You don't "defeat" it but you manage it. And at any moment it might consume you all over again. The boy isn't allowed to feed it at the end because like grief it can't be completed processed as a child.
A very Truman show-esque family style film which is comical from start to finish.
Shit was fucked up but I absolutely loved it. So hard to come across a good horror movie.