Which part? That God was God or that humans were His children? And are you talking about Adam and Eve and their children?
The original post, as you almost guessed, is about Adam and soon after, Eve, before the fall, when Adam was the son of God named in saint Luke's genealogy.
And Jesus himself was beginning to be about thirty years old, being (as it was supposed) the son of Joseph, who was of Heli, who was of Matthat, who was of Levi, who was of Melchi, who was of Jannai, who was of Joseph, who was of Mattathias, who was of Amos, who was of Nahum, who was of Esli, who was of Naggai, who was of Maath, who was of Mattathias, who was of Semein, who was of Josech, who was of Joda, who was of Joanan, who was of Rhesa, who was of Zerubbabel, who was of Shealtiel, who was of Neri, who was of Melchi, who was of Addi, who was of Cosam, who was of Elmadam, who was of Er, who was of Joshua, who was of Eliezer, who was of Jorim, who was of Matthat, who was of Levi, who was of Simeon, who was of Judah, who was of Joseph, who was of Jonam, who was of Eliakim, who was of Melea, who was of Menna, who was of Mattatha, who was of Nathan, who was of David, who was of Jesse, who was of Obed, who was of Boaz, who was of Salmon, who was of Nahshon, who was of Amminadab, who was of Aram, who was of Hezron, who was of Perez, who was of Judah, who was of Jacob, who was of Isaac, who was of Abraham, who was of Terah, who was of Nahor, who was of Serug, who was of Reu, who was of Peleg, who was of Eber, who was of Shelah, who was of Cainan, who was of Arphaxad, who was of Shem, who was Of Noah, who was of Lamech, who was of Methuselah, who was of Enoch, who was of Jared, who was of Mahalalel, who was of Cainan, who was of Enos,
who was of Seth,
who was of Adam,
who was of God.
Luke 3:23-38
And Christians are the children of the last Adam
Just as it was written that the first man, Adam, was made with a living soul, so shall the last Adam be made with a spirit brought back to life.
So, what is at first, not spiritual, but animal, next becomes spiritual. The first man, being earthly, was of the earth; the second man, being heavenly, will be of heaven. Such things as are like the earth are earthly; and such things as are like the heavens are heavenly. And so, just as we have carried the image of what is earthly, let us also carry the image of what is heavenly.
1 Corinthians 15:45-49
A long time ago, in the beginning, all human beings were Children of God; now all who are in Christ - the last Adam - are children of God.
