Praise the Lord (Psalms 117:1-2) that it is the spirit that matters not the flesh (John 6:63), that we need not concern ourselves with genealogies (Titus 3:9) for God is not a respecter of persons (Acts 10:34) but of faith, as it is that which He counts for righteousness (Romans 4:5).
Even as Abraham believed God, and it was accounted to him for righteousness. Know ye therefore that they which are of faith, the same are the children of Abraham. (Galatians 3:6-7)
Since Abraham is the father of all those who believe (Romans 4:11-12), we become children of Abraham through our faith and will sit down with him in the kingdom of heaven (Matthew 8:11), while the children of the kingdom (that is, of the physical seed or flesh) will be cast into outer darkness (Matthew 8:12) if they haven’t believed in the name of the only begotten Son of God (John 3:18).

In Romans, chapter 9 Paul is very clear about Israel, the seed of Abraham, and the children of God.
Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed. (Romans 9:6-8)
In John chapter 8, when Jesus is speaking to the Jews on the Mount of Olives He acknowledges that they are Abraham’s seed (John 8:37) but not Abraham’s children (John 8:39) as they sought to kill him (John 8:40). He further confirms that being the physical seed of Abraham is not what matters when he tells them that God is not their father (John 8:42) but, rather, that they are of their father the devil (John 8:44).
When we are saved by grace through faith (Ephesians 2:8) we are born again in the spirit (John 3:6) and become sons of God (Romans 8:14).
The Spirit itself beareth witness with our spirit, that we are the children of God: And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. (Romans 8:16-17)
Praise the Lord that it is the spirit that matters not the flesh.