children born not of blood, nor of the desire or will of man, but born of God.
These children are born of God, not by bloodline, human desire, or human will.
The verse defines the source of this new birth.
6There came a man who was sent from God. His name was John. 7He came as a witness to testify about the Light, so that through him everyone might believe. 8He himself was not the Light, but he came to testify about the Light. 9The true Light, who gives light to everyone, was coming into the world. 10He was in the world, and though the world was made through Him, the world did not recognize Him. 11He came to His own, and His own did not receive Him. 12But to all who did receive Him, to those who believed in His name, He gave the right to become children of God — 13children born not of blood, nor of the desire or will of man, but born of God.