The Wild Things are how Max views himself and the people around him.Each one of the Things is either part of his personality, or someone in his life as represented in his little mind.
Max's mom works for PixarWe hear her talking on the phone in one scene to a Mr. Lasseter. Perhaps she's taking a break from work?
Max had been kidnapped by a group of pedophilesThe Wild Things are just his image of them. They are a group of immature men and women who have nefarious plans, but they never got past the stage of giving Max everything he wants before Max escapes. If he would have stayed, he would have ended up "eaten" just like the other kids before him.
The Wild Things are Max's way of coping with his parents' divorce.Specifically, Carol, a male Wild Thing who's immature and selfish but speaks with the voice of an adult man, is Max's dad and KW, a female who speaks with the voice of a mature and motherly adult woman, is Max's mom. Notably, Carol is incredibly resentful of KW for meeting new friends, the same way Max's mom seems to be interested in another man. And at one point near the end, Carol becomes incredibly angry and Max, and he lashes out violently, the way a father with too big a temper would lash out at a son who disappointed him. A bit later, Carol calms down a bit and manages to have a tense-but-meaningful conversation with KW, asking very soberly, "Am I as bad as he says I am?" or in other words, "Am I really a bad dad?" KW says just enough to placate him, and when he leaves, Max (who is literally inside her belly at this point — talk about your Freudian imagery) reminds her that Carol "really does love [her]," which only leads her to muse that "it's hard being a family sometimes." The language and the imagery are really overwhelming.
Max didn't get out of K.W.'s Stomach.She kept him in there and the rest of the movie was his dying hallucination.