Why are Jem and Scout so welcome at the First Purchase Church in To Kill a Mockingbird?

First of all, Jem and Scout are the guests of Calpurnia,
one of the church's most stalwart members. Secondly, they are the children of Atticus
Finch, who is not only defending Tom Robinson, but (we find out later) is highly
respected in the black community. Additionally, because of the Jim Crow laws established
in the Deep South, and the manner in which African-Americans were mistreated by white
authorities, it would not be a wise decision for a group of black adults to make the
children unwelcome--even if they were the only white people at the church.
Repercussions, not by Atticus, but by other white members of the town, could have been
severe. Except for one person, Lula, who voiced her displeasure over Jem and Scout's
appearance, the members of First Purchase Church seemed to be a peaceful, friendly and
Christian group. Calpurnia would not have taken the children had she not already
realized the positive reception they would receive.