Satan's children are not in the physical sense. Satan can't create life. It is in the spiritual sense. Sort of like how Abraham has some descendants that are physical and some that are spiritual. Believers in Christ are spiritual descendants of Abraham because they have the same kind of faith that Abraham had.

From John 8: (Christ speaking to his enemies.) The Children of the Devil …43Why do you not understand what I am saying? It is because you are unable to accept My message. 44You belong to your father, the devil, and you want to carry out his desires. He was a murderer from the beginning, refusing to uphold the truth, because there is no truth in him. When he lies, he speaks his native language, because he is a liar and the father of lies. 45But because I speak the truth, you do not believe Me!…

When you observe someone speaking a torrent of lies, that is a big clue there.

From 1 John 3:

7 Dear children, do not let anyone lead you astray. The one who does what is right is righteous, just as he is righteous. 8 The one who does what is sinful is of the devil, because the devil has been sinning from the beginning. The reason the Son of God appeared was to destroy the devil’s work. 9 No one who is born of God will continue to sin, because God’s seed remains in them; they cannot go on sinning, because they have been born of God. 10 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.

(Brothers and sisters in Christ. All of humanity are our fellow man, and we should do good to others, but not all are brothers and sisters.)

More on Love and Hatred

11 For this is the message you heard from the beginning: We should love one another. 12 Do not be like Cain, who belonged to the evil one and murdered his brother. And why did he murder him? Because his own actions were evil and his brother’s were righteous. 13 Do not be surprised, my brothers and sisters,[b] if the world hates you. 14 We know that we have passed from death to life, because we love each other. Anyone who does not love remains in death. 15 Anyone who hates a brother or sister [in Christ] is a murderer, and you know that no murderer has eternal life residing in him.

Cain's physical father is Adam. His spiritual father is Satan. God did not adopt Cain as one of his children. All of us are God's creatures, as in "Preach the Gospel to every creature." When we first believe the truth concerning Christ, then we can know the Father has adopted us as his beloved children. All of God's children are saved.

The sheep are only temporarily lost because all are born spiritually dead, but even so, sheep are eternally saved through the Person and work of Christ. Christ undertakes, as the Good Shepherd, to search out all of his lost and straying ones. It is an absolutely secure salvation because it depends not in any way or part upon us. It is 100 percent the work of God in Christ with no contribution whatsoever from the sinner. If it depended upon you to any degree, well, you would never make it, because God requires absolute perfection of righteousness.

Perfection is found only in the work that Christ did to redeem his people from sin. God in Christ joined himself to our humanity in order to have the right of redemption, and he perfectly fulfilled the Law of God, being obedient, even unto death, as the only One who had the ability to pay our sin debts in full through his death and the shedding of his blood, which cleanses us from all unrighteousness.

The self-righteous unsaved, who despise the blood of Christ, well, they are called goats in scripture, which is one of many symbols of Satan. I don't worry much about this. God will do what is right and just because that is part of his perfect character.