His parentage depends on whether you are Sumerian or Babylonian. It could be APSU and TIAMAT or ANSHAR and KISHAR. Whoever. He himself had two sons, EA and ENLIL, and they all played dice to decide who did what. EA won the Sea, ENLIL the Land and ANU was left with the Sky.
Then they decided the Universe would make a good prize. This was a mistake as MARDUK, landlord of the Sun at that time, took objection and chopped ANU to bits.
So ANU became a bit of a nonentity, and as no-one knew which bits to bribe, he was used as a God of Judgment. Not that anyone took much notice. It was easier to roll dice.