Τεκνίον, little child, diminutive of τέκνον child, occurs in Joh 8:33; 1Jo 2:12, 1Jo 2:28; 1Jo 3:7, 1Jo 3:18; 1Jo 4:4; 1Jo 5:21. This particular phrase is found only here (best texts omit my in 1Jo 3:18). Used as a term of affection, or possibly with reference to the writer's advanced age. Compare Christ's word, παιδία children (Joh 21:5) which John also uses (1Jo 2:13, 1Jo 2:18). In the familiar story of John and the young convert who became a robber, it is related that the aged apostle repaired to the robber's haunt, and that the young man, on seeing him, took to flight. John, forgetful of his age, ran after him, crying: “O my son why dost thou fly from me thy father? Thou, an armed man, - I, an old, defenseless one! Have pity upon me! My son, do not fear! There is still hope of life for thee. I wish myself to take the burden of all before Christ. If it is necessary, I will die for thee, as Christ died for us. Stop! Believe! It is Christ who sends me.”
I write
More personal than we write (1Jo 1:4), and thus better suiting the form of address, my little children.
If any man sin, we have
The change from the indefinite third person, any man, to the first person, we have, is significant. By the we have, John assumes the possibility of sinful acts on the part of Christians, and of himself in common with them, and their common need of the intervention of the divine Advocate. So Augustine: “He said, not 'ye have,' nor 'ye have me,' nor 'ye have Christ himself;' but he put Christ, not himself, and said 'we have,' and not 'ye have.' He preferred to place himself in the number of sinners, so that he might have Christ for his advocate, rather than to put himself as the advocate instead of Christ, and to be found among the proud who are destined to condemnation.”
An advocate (παράκλητον)
See on Joh 14:16.
With the Father (πρὸς τὸν πατέρα)
See on with God, Joh 1:1. An active relation is indicated. On the terms the Father and my Father, see on Joh 4:21.
The righteous
Compare righteous, 1Jo 1:9. There is no article in the Greek. Jesus Christ righteous. See on 1Jo 1:9.