1 John 3:10

By this it is evident who are the children of God , and who are the children of the devil : whoever does not practice righteousness is not of God , nor is the one who does not love his brother .

This is how we know who the children of God are and who the children of the devil are: Anyone who does not do what is right is not God`s child, nor is anyone who does not love their brother and sister.

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.