Child murder is pretty obvious in this case, because the story is about a father who kills his three children.
Mental disease
The father of the three children is suffering from a mental disease, and tells his story to a psychiatrist.
The father tells the psychiatrist that it is a boogeyman that killed his children, but the reality is that he did it himself and that tells us that maybe is suffering from a split personality.
At first it seems like that the story belongs to Todorov's categorie the Fantastic because we accept that the monster is a "real" thing, but as we keep reading we realize that the father is suffering from a mental disease and that the boogeyman is in his imagination, and the story ends under the categori The Uncanny.
Excellent analysis - you bring Todorov's categories into it nicely in a way that makes sense.
SvarSlet