Below are things that may ruin the movie for you if you haven't seen it already, so avoid reading it unless you've seen it, or want to taint your movie-going palette with stuff you shouldn't really know going in...
This whole movie is obviously the fantasy of the boy. We see every element of the film set up within the first ten minutes of the narrative, while Kevin lives in the "normal" world. All the places he visits we see are illustrated in his readings, drawings, and toys he surrounds himself with. He is always recognized by the group of bandits, both in terms of attention and for his good ideas. But it comes down to the oppressive life that his parents make him live. They are ultimately personified in the embodiment of Evil, down to the striving for perfection through technology and the plastic-wrapped furniture. In the end, both are destroyed. But it is a thing that still bothers me, as I cannot get the reasoning behind the final scene where his parents are destroyed by Evil. I guess it comes down to the wink by the fireman, the "real" embodiment of King Agamemnon. Does it imply that, as in his fantasy world, he will find a new father-figure that he respects that will adopt him? Since there is an obvious transition back to the "real" world, I can see it as his rationale for accepting their deaths in the fire. But it's too vague, and ultimately just kinda pisses me off. Too bad, cuz I love the rest of the movie.