John was an elderly man and their leader. He used this expression to show his love for them. Alternate translation: "My dear children in Christ" or "You who are as dear to me as my own children" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The word "advocate" here refers to Jesus. Alternate translation: "we have Jesus Christ, the one who is righteous, who speaks to the Father and asks him to forgive us" (See: [[rc://en/ta/man/translate/figs-explicit]])