This girl is seriously a trip. She's a polished, polite, dignified, blue-blooded aristocratic lady – and she's only thirteen. Esmé is a proper lady (she has a noble title and everything), and she's very aware of it, thank you very much. However, the burden she bears is heavier than a simple honorific title – since she and Charles are orphans, she has to look out for both of them. Their mother died earlier (we're not sure how), and her father recently died in the war in North Africa. While Esmé and Charles live with a very kind aunt, we get the feeling that Esmé thinks she's become the default head of the family.
Esmé is a child who's forced to grow up before her time, but who still manages to retain a genuine sense of youthful innocence, despite her circumstances. Rather than becoming cynical and embittered by what life has dealt her, she somehow adopts an interesting front, half adult, half child. She thinks she's incredibly grown up, and her polished exterior reflects that (which is why she's so concerned about her wet hair when she meets the narrator). She's definitely a most impressive little figure, and though we're supposedly adults, we find her poise and social grace enviable. As the narrator notes with some surprise, she even looks like a little grownup, with her "blasé" eyes that seem, rather coldly, to observe everything.
However, Esmé is also clearly a kid on the inside, and that inner child escapes constantly. What's truly hilarious about her is the smooth, flawless way she delivers lines that only a child could think of. For example, the idea that she's "extremely interested in squalor" (79) is not anything you'd ever hear a real grownup admit (even if it's true). Less hilarious and more touching is the way in which Esmé's inner sadness emerges throughout the conversation, even when she doesn't realize it. She keeps bringing up her parents, especially her father, under the pretense that Charles is the one that desperately misses them – but we realize that she misses her mother and father tremendously herself. Esmé tells the narrator that she came over to talk to him because he looked lonely, and we have to wonder if it wasn't also because she was lonely, too.