The believers in Christ are children of God.

… Everyone who believes that Jesus is the Christ has been begotten of God… (1 John 5:1).

To be begotten means that we have become the children of God.

John’s writings on the mysteries of the eternal divine life stress very much the divine birth (3:9; 4:7; 5:1, 4, 18; John 1:12-13), which is our regeneration(John 3:3, 5). It is the greatest wonder in the entire universe that human beings could be begotten of God and sinners could be made children of God! Through such an amazing divine birth we have received the divine life, which is the eternal life (1:2)… (Excerpted from Holy Bible Recovery Version, note 7)

The eternal life we receive from God through regeneration, enables us to be God’s children and becomes the authority for us to be children of God (John 1:12-13).

Then the Spirit witnesses with our spirit that we who once were children of the Devil are now the children of God (Rom. 8:16).

See what manner of love the Father has given to us, that we should be called children of God; and we are. (1 John 3:1) 

To hear more on the divine birth and our abiding in God: