144,000 "of all the tribes of the children of Israel" has been understood to mean 144,000 "Jews" even though that's not what it says. The 12 tribes of the children of Israel were never called the "Jews." The word "Jew" was first used in 2 Kings 16:6 to refer to the two tribes of the southern kingdom, which were primarily from the tribe of Judah and were separate from the 10 tribes of the northern kingdom of Israel that had split off. Long story short, the northern kingdom became a mixed people called the "Samaritans." Longer story shorter, the 12 tribes of Israel simply don't exist today. So, who are these people? See Revelation 14:1-5, specifically the notes after verses 1, 3 and 5.