we are not all children of God
He is Creator of us all
We can become one of His children…
But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name (John 1:12)
When we receive Jesus, we are adopted into His Family, grafted in, recreated as a new creature, and born again into the family of God, and we can then call Him Abba Father.
For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father. (Romans 8:15)
Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new. (2Cor 5:17)
Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God: therefore the world knoweth us not, because it knew him not. Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is. (1 John 3:1-2)