The tone of this story is what educational reform advocates from the 1950s would call "troubled." That's because we're seeing this whole thing through the eyes of the normal guy, Bartholomew Cubbins. And when you're the only non-crazy person in a castle, things get a little bit tense.
This tone shows up right from the beginning. Check out the italics here:
All summer when the sunshine came down, he growled at that…All summer when the fog came down, he growled at that…And that winter when the snow came down, he started shouting!" (5-7)
Both the italicized "that" and the exclamation points (which crop up throughout the narrative) express Bartholomew's exasperation. They scream: "Can you believe this guy?"
Bartholomew raises the bright red anxiety flag most urgently when he's waiting for the oobleck to arrive:
At first it seemed like a little greenish cloud…just a wisp of greenish steam. But now it was coming lower, closer, down toward the fields and farms and houses of the sleeping little kingdom. (37)
See how Seuss repeats the word "greenish" twice? See how he piles on descriptive and active verbs right next to descriptions of that innocent, sleeping little kingdom? This is Seuss's way of ushering the Big Bad into town. Danger looms around our sweet innocents, threatening to swallow them whole.
It's no wonder Bartholomew's anxiety and frustration continue as he rushes around trying to save everyone from the oobleck (or themselves), expressed later in all caps:
"Don't, Captain! DON'T!" (89)
Geez. Can't anybody lend this guy a hand?