Well, on one level you are right: The apostle Paul told the religious but pagan Athenians: "As some of your own poets have said, 'We are his offspring.'" (Acts 17:28)
So Paul did try to use that as a bridge as you have. On the other hand when it came to religious folks who are trying to righteously work their way into godhood (like temple-visting Mormons...about 20% of all Mormons) or religious folks relying on their own righteousness (like "Christians in Name only"...Jesus was harshest in discounting this idea. He told the religious Pharisees:
"'You brood of vipers! Who warned you to flee from the coming wrath?...do not think you can say to yourselves 'We have Abraham as our father.' I tell you that out of these stone God can raise up children for Abraham." (Matthew 3:7-9).
Now, of course, this wouldn't apply only to Mormons: It can apply to those who say "We have Joseph Smith as our spiritual father" AND it can apply to those who say "We have Calvin or Wesley or Luther or whoever as our spiritual father."
Jesus elaborated on this in John 8, where he told the Pharisees that "You belong to your father, the devil...you want to carry out your father's desire...You are doing the things your own father does." (John 8:44-45, 41).
So, since Mitt's recent "Mormon" speech twice used the concept that we are all "children of God" and you reiterate it here, I'm assuming you have bought into his religious propaganda...propaganda about some pre-existent spirit world that Mitt believes...propaganda that openly militates against what the Biblical Jesus taught.
It’s not propaganda, it is biblical doctrine.
Num. 16: 22 God of the spirits of all flesh.
Deut. 14: 1 Ye are the children of the Lord your God.
Mal. 2: 10 Have we not all one father.
Acts 17: 29 we are the offspring of God.
Rom. 8: 16 Spirit itself beareth witness . . . we are the children of God.
Eph. 4: 6 One God and Father of all.
Heb. 12: 9 ..be in subjection unto the Father of spirits.
These are just a few of the references in the Old and New Testaments that clearly indicate that God is our Heavenly Father. I believe the Bible. I believe the words of these ancient prophets. If you interpret the above differently than I, that is fine. I certainly will not bash you for it, and I would appreciate you not bashing me with a presumption that your interpretation is correct.