Floyd Mayweather -- Comforts 6-Year-old Boxing Phenom ... After Crushing Musical Chairs Defeat

Floyd Mayweather came to the rescue this weekend -- consoling a 6-year-old boxing phenom after the kid suffered a devastating defeat in a game of musical chairs ... and we've got the footage.

Floyd was sitting courtside at the 4th annual Ball Up Streetball Championship in Vegas on Saturday where a couple of kids participated in some musical chairs in between quarters.

The kid lost -- Floyd jumped out of his seat and gave the kid a hug. It was a very nice moment.

But get this ... the kid is a serious boxing prodigy!!! His name is Famous J and he trains with Floyd's uncle Roger Mayweather ... and he's QUICK!!!

Check out the clip -- the kid's got some serious potential (not in musical chairs tho).