The Greek behind this text is as follows (Received Text - Stephens, Elzevir, Beza and Scrivener all read exactly the same) :
πας ο πιστευων οτι ιησους εστιν ο χριστος εκ του θεου γεγεννηται και πας ο αγαπων τον γεννησαντα αγαπα και τον γεγεννημενον εξ αυτου
It is important to notice that neither 'child' nor 'children' is in the Greek text. The word used is 'begotten', γεγεννημενον. It appears as a participle - a verb-form used in noun-form - and has the definite article attached, τον 'the'.
So the correct translation ought to include the words 'the begotten'.
The agent is singular, as is the predicate singular, that is to say the subject of the sentence 'every one (singular)' and the object of the sentence 'loveth the begotten (singular)' both correspond grammatically.
The wording τον γεγεννημενον, the begotten, is accusative singular, both the article and the noun. The accusative plural would end in ους, not ον.
The KJV renders the text as follows :
Whosoever believeth that Jesus is the Christ is born of God: and every one that loveth him that begat loveth him also that is begotten of him. [KJV 1769].
The KJV is not unique in this presentation :
'... doth love also him that is begotten of him' Young's Literal.
'... loves also the having been born of him' Green's Literal (but 'born' is not quite the same as 'begotten', I would point out).
'... loves also him that has been begotten of him' EGNT (The literal interlinear of the Englishman's Greek New Testament - Bagster.)
'... loveth him also which is begotten of him' Tyndale.
'... loves also him that is begotten of him' J N Darby.
Translations from the Latin Vulgate :-
'... loves him that is born of him' The Wycliffe (again, 'born' is not quite correct for τον γεγεννημενον. Wycliffe uses 'gendered', correctly, in the first half of the verse.
'... loveth him also who is born of him' Douay Rheims. (Again, perhaps the Latin re-translation has influenced the loss of the specific meaning of τον γεγεννημενον.)
John speaks of one who is begotten of the Father. And he says that everyone who loves him that begat - loves also him that is begotten of him. Or, to be even more literal :
... (loves) also the begotten out of him
... (αγαπα) και τον γεγεννημενον εξ αυτου
This love would include the love of Jesus Christ, for the Son is begotten of the Father. And this love would also include any individual who is born of God with a second birth - a birth not of nature, but from above.
John's use of the wording 'the begotten' includes both him who is everlastingly begotten (the begetting of the Father in One Spirit of the Son of God, eternally) and also him who is born of water and of spirit, a 'new' birth, an 'again' birth, a birth 'from above'.
It appears to me that some translations are paraphrasing John's words and it appears to me that something quite significant is being lost in translation.
