Why does Calpurnia arrive at the courthouse in Chapter 20 of To Kill a Mockingbird?

At the end of Chapter 20, Calpurnia makes her way to Atticus, who has just given his closing remarks. Calpurnia politely asks Judge Taylor if she could pass a note to Atticus. Calpurnia delivers a note written by Aunt Alexandra, which says the children have been missing since noon. Mr. Underwood tells Atticus that Jem, Scout, and Dill are sitting in the Colored balcony, and they've been there since noon. Atticus then calls for Jem to come down, and the children climb across Reverend Sykes to make their way toward Atticus. Scout mentions that Calpurnia looked "peeved," but Atticus appeared to be exhausted. Atticus tells the children to return home with Calpurnia, which Jem protests. Atticus allows the children to return to hear the verdict after they eat their supper. Calpurnia then walks the children home and yells at Jem for taking Scout to see the trial.