Can people belonging to faiths other than Christianity claim to be God's children? Are Buddhists, Hindus, Muslims and Atheists God's children?
Paul told the Christians at Rome that the presence of the Holy Spirit made them God's children. (Romans 8:16) Likewise, he told the saints of Galatia that they were God's children because of their faith in Christ Jesus. (Galatians 3:26)
However, Christ did say that peacemakers would be called God's chilren. (Matthew 5:9) He also suggested that the Jewish religious leaders of his day were Satan's children. (John 8:38-44) John wrote: "In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother." (I John 3:10) So we see that these scriptures clearly imply that those who do righteous things are God's children and those who do wicked things are not his children.
Nevertheless, there is also a sense that everyone on this planet has fallen short of God's perfection and sinned in the course of their lifetimes. (Romans 3:23) We could also say that everyone on this planet has fallen under Satan's sway to one degree or another. (Revelation 12:9)
If Satan has deceived the whole world, doesn't that mean everyone - including Christians? Didn't Paul say that we (Christians) see through a glass darkly? (I Corinthians 13:12) So does being less deceived that someone from another faith give us bragging rights over them? Does being a Christian secure us a greater place in God's affection? Or does being a Christian mean that we are a sinner saved by the grace of God? Didn't Christ die for the sins of the whole world? (I John 2:2)
Just before Christ ascended into heaven, he instructed his apostles to make disciples of all nations. (Matthew 28:19) When Peter finally realized that God wanted the Gentiles to hear the gospel message, he declared: "I see very clearly that God shows no favoritism. In every nation he accepts those who fear him and do what is right." (Acts 10:34-35, NLT)
When Luke recorded Christ's genealogy in his gospel account, he listed Adam as the son of God. (Luke 3:38) Hence, if we are all the sons and daughters of Adam (Deuteronomy 32:8 and Acts 17:26), doesn't that makes us all God's children too?