A homeless man who body-slammed a 6-year-old boy in Queens on Thursday, leaving him with serious injuries, has been charged with assault, police said.

The vagrant — identified Friday as Laurance Gendreau, 35 — randomly attacked the boy, who was sitting on the steps of his grandparents’ home in Kew Gardens around 5:30 p.m., police said.

Gendreau grabbed the child, picked him up and slammed him face-first onto the ground.

He is charged with assault, harassment and acting in a manner injurious to a child, police said.

The child was taken to Cohen Children’s Medical Center and is in critical but stable condition in the intensive care unit, according to his grandfather, Naftali Portnoy.

“He has hemorrhaging, bleeding on the brain, concussions, [a] collapsed lung, [and] two skull fractures hopefully in places that can heal,” Portnoy told The Post. “They’re monitoring for seizures.”

“Just keep the family in prayers,” he added.

Gendreau was arrested on assault charges in January for allegedly throwing a chair at a woman during a dispute at a Manhattan restaurant, cops said.

He is undergoing psychiatric evaluation at Jamaica Hospital Medical Center, according to police.

Sources said he has a history of mental illness.