I came across the following translation and I was unsure why the sentence started with "de"
Little girls read books.
De petites filles lisent des livres.
In this sentence, de is the plural form of the indefinite article. It means that some little girls read books.
Usually the plural indefinite article is des. However it becomes de in two cases:
The English sentence could also mean that little girls in general (i.e. all or at least many little girls) read books. This meaning would call for a definite article: “Les petites filles lisent des livres”.