Ironically, it is the children who are more imaginative, clever, and objective than the petty, pontificating, self-affirming aunt.
The main conflict in "The Lumber Room" revolves around the myopic perceptions of the "soi-distant aunt." When Nicholas announces that there is a frog in his bread-and-milk, his aunt is so short-sighted and ignorant of the antics of mischievous boys that she cannot imagine a frog getting into the boy's bowl, so she refutes Nicholas's claim with pontification, declaring that there cannot possibly be a frog in his bowl.
Nicholas, then, is punished for his "sin of taking a frog from the garden and putting it into a bowl of wholesome bread-and-milk"; in fact, his mischief is magnified because the "older, wiser" adult has been proven to be "profoundly in error in a matter about which [she] has expressed supreme confidence." It is her pettiness that raises the ire of the clever Nicholas, who determines to outsmart her later by manipulating circumstances to his advantage where he can manipulate her own orders against her. For, when she falls into the water tank and calls out to Nicholas to help her, he reminds the aunt that he was given strict instructions not to enter the garden. So, she rescinds her order, but the imaginative Nicholas retorts,
"Your voice doesn't sound like aunt's," objected Nicholas....Aunt often tells me that the Evil One tempts me and that I always yield. This time I'm not going to yield."
Then, he tricks her into admitting that there is strawberry jam that he may have with tea so that he can affirm that she must, indeed, be the Evil One since his aunt has told him earlier that there was none. After this, Nicholas abandons her and the aunt is only later rescued by a servant.
The aunt, of course, "was a woman of few ideas, with immense powers of concentration," but Nicholas has enjoyed adventures of the imagination in the Lumber Room and "an unusual sense of luxury in being able to talk to an aunt as though one were talking to the Evil One...." With "childish discernment," though, he does not over-indulge.