This video has been making the rounds. I received it in an e-mail from my cohort Stan. After a little research, I discovered the name of the group and ages of the players:
Michael (8) and Sullivan (10) play a bluegrass version of El Cumbanchero on mandolin and guitar with sister Molly (16). The photo above shows them with bluegrass legend, Ralph Stanley.
Check out their father's website for more info and visit Molly's website for her music and a list of her appearances.