So who are children of Israel today?

 In the day when God shall judge the secrets of men by Jesus Christ according to my gospel. Romans 2:16

Behold, thou art called a Jew, and restest [second-person singular simple present form of rest] in the law, and makest thy boast of God, Romans 2:17

For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh Romans 2:28

But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God. Romans 2:29

Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: Romans 9:6

Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. Romans 9:7

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 9:8

Even as Abraham believed God, and it was accounted to him for righteousness. Gal 3:6

Know ye therefore that they which are of faith, the same are the children of Abraham. Gal 3:7

But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into His marvelous light; 1Peter 2:9

Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy. 1Peter 2:10

Yet, we are admonished to gather together in worship, without compromising Scripture.  

To the law and to the testimony: if they speak not according to this word, it is because there is no light in them. Isaiah 8:20

We worship together with those who find light in the Word of God and not in the traditions and directives of men.

For where two or three are gathered together in my name, there am I in the midst of them. Matt 18:20

Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching. Hebrews 10:25