According to the Talmud God's statement to Moses actually came true, so we just have to check what they are actually called.
Berachot 7a
וא"ר יוחנן משום ר' יוסי כל דבור ודבור שיצא מפי הקב"ה לטובה אפי' על
תנאי לא חזר בו מנא לן ממשה רבינו שנא' הרף ממני ואשמידם וגו' ואעשה אותך
לגוי עצום אע"ג דבעא משה רחמי עלה דמלתא ובטלה אפ"ה אוקמה בזרעיה שנא'
בני משה גרשום ואליעזר ויהיו בני אליעזר רחביה הראש וגו' ובני רחביה רבו
למעלה וגו' ותני רב יוסף למעלה מששים רבוא אתיא רביה רביה כתיב הכא רבו
למעלה וכתיב התם ובני ישראל פרו וישרצו וירבו
R. Johanan further said in the name of R. Jose: No word of blessing
that issued from the mouth of the Holy One, blessed be He, even if
based upon a condition, was ever withdrawn by Him. How do we know
this? From our teacher Moses. For it is said: Let me alone, that I may
destroy them, and blot out their name from under heaven; and I will
make of thee a nation mightier and greater than they. Though Moses
prayed that this might be mercifully averted and it was cancelled,
[the blessing] was nevertheless fulfilled towards his children. For it
is said: The sons of Moses: Gershom and Eliezer . . . And the sons of
Eliezer were Rehabia the chief . . . and the sons of Rehabiah were
very many. And R. Joseph learnt: They were more than sixty myriads.
This is to be learnt from two occurrences of the term ‘manifold’. Here
it is written: were very many, and elsewhere It is written: And the
children of Israel were very fruitful and increased abundantly, and
became very many. (Soncino translation)
According to this passage, then, the name is בני רחביה (Children of Rechavia).