Expressions of thankful joy are common in the Pauline salutations. See Romans, 1 Corinthians, Ephesians, Philippians, Colossians, 1 Thessalonians, 2 Thessalonians, Philemon.
Greatly (λίαν)
The word is found in John's writings only here and 3Jo 1:3.
I found (εὕρηκα)
See on Joh 1:41. Rev., I have found.
Of thy children (ἐκ τῶν τέκνων)
The rendering is obscure. Rev., rightly, supplies certain. Compare Joh 16:17.