A Brooklyn grand jury is weighing whether to indict a 15-year-old alleged gangbanger for the Labor Day mass shooting that shattered a 6-year-old’s femur and injured five others, it was revealed Friday during a court hearing.

Baby-faced Donovan Bailey appeared via video from the Crossroads Juvenile Center wearing a blue surgical mask — but did not utter a word during the brief proceeding.

One of his lawyers, Brian Buckmire, said his client did not want to testify before the grand jury, which was in session Friday. Another attorney, Hermann Walz, who was also on the video conference, represents Bailey on a first-degree robbery case from July 2019. The judge, prosecutors and lawyers all appeared via Skype.

Assistant DA Anthony Bailey (who is no relation to the defendant) asked the judge to remand him on the earlier case, for which he had been released without bail, in light of the serious new arrest.

But Judge Craig Walker said he’d wait to make a ruling until the end of the day after he learns whether the grand jury returns an indictment for the Sept. 7 shooting in Crown Heights that occurred after 2 a.m. during an unsanctioned J’Ouvert celebration.

The exact charges that grand jurors are considering were not disclosed, but Donovan Bailey was arrested on attempted murder, assault and weapons possession raps for the gunfight that authorities say stemmed from a gang dispute.

The alleged teen triggerman, who is a reputed member of the Crips, has 12 prior arrests. He’s also being eyed as the killer in a Sept. 5, 2019, murder in East Flatbush, according to Chief of Detectives Rodney Harrison.