It sounds like a pretty harsh characterization, but it serves a purpose in "Barbie Doll." The girlchild's "fat nose on thick legs" sounds extra-mean so that we can feel for a minute the kind of pressure and humiliation the girl experiences. And this kind of pressure isn't hers alone. Countless girls in America undergo similar kinds of absurd expectations, no matter how wonderful these girls may be on the inside. This poem points to how society tends to value the book's cover over the book when it comes to women, but hopefully smart Shmoopers will change all that.
Lines 5-6: Those first classmates who point out the girl's so-called imperfections kind of set the standard for everyone else. No matter how foolish they may sound, they mirror the kinds of superficial values that the adult world likes to encourage.
Lines 10-11: The "fat nose on thick legs" is all everyone ever sees. So they sound brainwashed since they can't see all of the wonderful attributes the girl actually has. They're a bit like Barbie zombies looking for noses and legs to eat, rather than brains.
Lines 17-18: As gruesome as it sounds, the girl cutting off her nose and legs serves as a kind of symbol for the absurdity of the adult world's superficial values. By pressuring young girls, we essentially kill their natural spirit and prevent them from being who they are. Bad news.