In Romans 9, who counts as the true children of the promise?

According to Romans 9, the true children of the promise are not all Abraham's descendants. They are specifically those who came through Isaac, Jacob, and the twelve tribes. Ishmael, though blessed, was not included in the covenant line; God established His covenant with Isaac.

Les teaches that not all of Abraham's children are children of the promise. Ishmael, though Abraham's son, was blessed: God promised to make him fruitful, multiply him exceedingly, give him twelve princes, and make him a great nation. Les notes the Arabs outnumber the Jews 50 to 1 and possess the world's oil, evidence God blessed Ishmael. But the covenant line runs only through Isaac, Jacob, and the twelve tribes. God told Abraham His covenant would be established with Isaac, whom Sarah would bear at the set time.

Romans 9:6

Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel:

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Are all the descendants of Abraham children of the promise?

No. Scripture distinguishes Abraham's descendants from children of the promise. Ishmael was blessed and made fruitful, a great nation with twelve princes, but God established His covenant with Isaac, whom Sarah would bear. Only those descending through Isaac, Jacob, and the twelve tribes are counted children of the promise.