John Gill Commentary 2 John 1:13

"The children of thine elect sister salute thee." — 2 John 1:13 (ASV)

The children of your elect sister greet you. Amen .
Not the members of a sister church, as some think; but the children of one who was the sister of this lady, according to the flesh; and who, as she was either a very famous and excellent person, or rather one chosen of God likewise unto eternal life and salvation; and whose children also were walking in the truth, and here send their Christian salutation to their aunt; very likely those sister's children lived at Ephesus, where John resided.