Great Plains people who call themselves "Children of the Middle Waters" (5)

I believe the answer is:

osage

(Other definitions for osage that I've seen before include "member of tribe" , "Native Americans from Missouri - age so (anag)" , "Brave" , "Member of the Native American people, once occupying the Missouri valley" , "American Indian" .)

I've seen this clue in the LA Times.

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