In Chapter 7 we learn a little background on the Bennets. And we learn that Mrs Bennet has a brother and a married sister (Mrs Phillips). Mrs Phillips is evidently a bit of a gossip, because

"however bare of news the country in general might be, they [Kitty & Lydia] always contrived to learn some from their aunt [Phillips]."

JA also tells us more explicitly that Kitty & Lydia are the silliest of the Bennet daughters. After mentioning the close distance (1 mile) of Meryton to Longbourne, and that the Bennet girls frequently visited there, the narrator says that the

"Catherine and Lydia, were particularly frequent in these attentions; their minds were more vacant than their sisters', and when nothing better offered, a walk to Meryton was necessary to amuse their morning hours and furnish conversation for the evening"