My friend, I think that ever since Abraham was born it has been the same.
The true children of Abraham have his faith, and are the redeemed in Christ, both new and old.
God has always had a special regard for the physical children too, including children of all believers, but they must be found faithful to have His blessing.
Under the old covenant it was still the kingdom of Christ though Jesus had not yet come to redeem it.
When Job says: "For I know that my redeemer liveth, and that he shall stand at the latter day upon the earth:"( Job 19:25), he is speaking of his faith in Jesus, through which he becomes a spiritual child of Abraham, for ever.
Jew? Gentile? If our father is God it is one and the same.
In the NT we are all named after Jacob (Gal 6:16), after Isaac (Rom 9:7) and after Abraham (Gal 3:29).
We are even all called Jews, but in the spiritual sense (Romans 2:28).
We prefer to name ourselves after Christ for good reason, because through Him we call God our Father.
In the OT they named themselves after Jacob also for good reason.
Israel is the name of a man who wrestled with God and yet prevailed.
That can only be done through Christ, so the true kingdom of Israel is the kingdom of Christ.
I never heard of "the kindom of Christ." Could you please explain? Scriptures given from the bible will be helpful, especially we are bible believer. Anything not from the bible comes from Satan.