Other than the fact that they did not know where the children were, why were Calpurnia and Aunt Alexandra so upset that the children were attending the trial?
Atticus had directly told the children not to attend the trial, a decision that Calpurnia and Aunt Alexandra fully supported. All three adults knew that the trial would bring out the worst in the townspeople, people that the children knew and admired. They wanted to shelter the children for as long as possible against the hatred and prejudice of the people. Calpurnia and Alexandra also both know the stress and pressure on Atticus. They know that protecting the children and keeping them away from the trial will give Atticus one less thing to worry about.