His name is Walter. Check the following scenes that relate to Walter:
1. Scout has a conversation with Mr. Cunningham when he brings hickory nuts as payment for Atticus' legal service. She learns about "entailments."
2. Scout gets in a fight with Mr. Cunningham's sone, Walter, her first day of school because she got in trouble for telling the teacher that the Cunninghams are too proud to take anything from anyone. Jem invites Walter to come home with them for lunch to make up for Scout's behavior.
3. When the mob threatens Atticus at the courthouse, Scout recognizes Mr. Cunningham, reminds him that she is friends with his son, Walter, and her action makes the mob calm down and disperse, thus saving Atticus from possible violence.