I've done some additional research and wrote to the orphanage where Charles, Mary, and Arthur were living in 1900. They are not the children of Erhart and Anna. I had made the same assumption until I contacted someone who is related to one of Erhart and Anna's children.
Erhart and Anna's children were: Anna, Bertha, Rose, Frances, Charles (not the one you found)and their was a child named John born about 10 days before Anna's death. I am the grand daughter of Frances.
I have additional information. Contact me at email@example.com