I recently read it again as an adult and I found it disturbing. I think I the monster doesn't exist, or at least the monster isn't what he seems. Throughout the book his mum and dad ignore Bernard despite him telling hem there is a monster in the garden but they react as if they hear this kind of stuff daily and shrug him off until he goes and talks to the "monster" but he monster gobbles him up. I think this is a metaphor, Bernard is a neglected child and neglected children act up a d when the monster enters the home he does all the things Bernard would have except he makes a mess of his food, destroys his toys and bites his dad in the same way a neglected child would act. Then at the end he goes to bed with Bernards teddy and says to his mum "but I'm a monster" to which she replies "not now Bernard".

I decided to reread it after I thought about how messed up it was that he was just ignored by his parents and once I had read it again I saw it in a different light. Bernard is a problem child who becomes a monster because of neglect.