25 The one who practices righteousness. The participle (ὁ ποιῶν, ho poiōn) + noun constructions in 3:7 and in 3:8a, the first positive and the second negative, serve to emphasize the contrast between the true Christians (“the one who practices righteousness”) and the opponents (“the one who practices sin,” 3:8a).
26 Grk “that one.” Context indicates a reference to Jesus here. As with the previous uses of ἐκεῖνος (ekeinos) by the author of 1 John (2:6; 3:3, 5), this one refers to Jesus, as the reference to “the Son of God” in the following verse (3:8) makes clear.

In other versions

Little children, let no one deceive you. Whoever practices righteousness is righteous, as he is righteous.

Dear children, do not let anyone lead you astray. The one who does what is right is righteous, just as he is righteous.

Little children, let no one deceive you. The one who does what is right is righteous, just as he is righteous.

Dear children, don’t let anyone deceive you about this: When people do what is right, it shows that they are righteous, even as Christ is righteous.

Little children, let no one deceive you: the one who practices righteousness is righteous, just as that one is righteous.

Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous.

Public Domain