Hawthorne does this on purpose to give the reader a hint as to the supernatural and otherworldly character of Pearl, the daughter born out of an adulterous affair to Hester and the Puritan Pastor. In Chapter VI, when we really focus on the little girl, there are descriptions of her nature--she truly is more comfortable away from people, in the forest decorated with flowers and leaves as an elf or fairy child would be. She is incredibly smart as Hester was at Pearl's age, and the girl detects that it is society's fault that she and her mother are forced to live on the edge of society and secluded. Therefore, it is only natural that she is hostile toward society for putting her beloved mother in this position.
In this same chapter, Hester asks Pearl, "Child, what art thou?" and her next question is "Art thou my child, in very truth?" These questions follow Pearl's abnormal laughter, actions in the forest, her wild and black eyes, and the way she seems to bond with the sun shining between the leaves of the trees, the water in the brook and the wildflowers. Hawthorne describes her as dancing
"up and down, with the humorsome gesticulation of a little imp whose next freak might be to fly up the chimney...such was Pearl's wonderful intelligence that her mother half doubted whether she were not acquainted with the secret spell of her existence, and how she might reveal herself".
He is attempting to give her magical, unnatural qualities due to the circumstances of her unnatural birth. It is similar to the immaculate conception of the Virgin Mary, but in a negative connotation since Hester's pregnancy was caused by a man who is not her husband.