B2K Brings Out Secret Weapon Against Pretty Ricky in Verzuz

B2K went to their secret weapon in a music battle against Pretty Ricky ... bringing out an 11-year-old on stage for a mega-boost ... Omarion's son, Megaa.

Check out the video ... B2K was rockin' the floor at Verzuz Thursday night, playing their popular song "Understanding." See that young face in the group? That's Omarion pre-teen son.

This kid can definitely hang with the grownups ... he had a flow just like his pops, and completely took over the show!

Unfortunately, Megaa's addition wasn't enough to get the win against Pretty Ricky, who swept B2K in the boy band battle ... but from a vocal standpoint, Megaa held his own.

The showdown took place in front of celebs like Lizzo, Scrappy, and Trick Daddy ... and Omarion's offspring clearly wasn't feeling any stage fright in the presence of some music royalty.