Carmelo Anthony's -- 2nd Grade Son ... Dominating 3rd Grade Basketball

Carmelo Anthony's son is a BEAST on the court -- and he's only 8 years old ... with his youth team crushing it in a 3rd grade national tournament ... despite the fact they're only 2nd graders.

TMZ Sports has learned ... Melo's son Kiyan is a member of the New York Gauchos -- which competed at the elite AAU Nationals this weekend in Orlando.

We spoke with NYG's basketball director, Maxwell Cole, who told us the team is so good, they're competing against bigger and older kids and WINNING!

In fact, Cole says the Gauchos finished 9th overall -- impressive considering how many 3rd grade AAU teams there are in the country!!!

As for Kiyan, Maxwell tells us he's great -- and seems to be getting better every day.

"He knows the game. You can tell the influence his dad has on him. You know he comes from a basketball family."

Both Melo and LaLa were in the stands cheering on their son (who wears #7 like his dad) ... and we're told Shaquille O'Neal also stopped by to support the kids!