Yoru Naku Suzume

Children have been disappearing mysteriously and it has been a major concern to many parents. One parent is found wandering about the streets asking people if they've ever heard of the swallow that cries at night. A waitress who works at a bar guides her to the bar and allows her to discuss her situation. In the bar, the waitress, a bartender, and a little girl listen. Once she has finished talking, she leaves. Now all the waitress and bartender has to do is wait. The little girl disappears from the bar and she appears on the streets. She finds and traces the girl in question and follows her to discover...?

(Source: MangaHelpers)