A 13-year-old boy has been charged with assault after he allegedly stabbed and left his older sister, 14, in critical condition on Saturday, March 11, in their home in Jamaica, Queens, New York.

The children’s mother Rupiah Begum, 42, said she’s at a loss to understand what came over her typically amicable son.

“I don’t know what happened,” Begum told The Post from her Jamaica home on Sunday, March 12.

“Everything is good usually. They play together. No problems usually.”

The mother of five said her son, whose name is being withheld, was “frightened” and speaking to detectives at the 113th Precinct stationhouse while her daughter, who suffered multiple stab wounds, remained at Jamaica Hospital in critical condition.

“He said something is wrong,” Begum said of her son. “He said he was angry.

“He stabbed her multiple places, multiple times,” the mom said. “I don’t know what happened.”

Begum said she was at work at McDonald’s about five minutes from the family home at 11th Avenue and 156th Street when she got the call that her son allegedly stabbed her daughter around 7 p.m. on Saturday, March 11.

“I was not home. I was called away. An emergency at work,” she explained.

She said her husband, who neighbors said drives a cab and owns a taxi service, is away on a trip to Bangladesh.

Police said the teen got into a beef with his sister and stabbed her with a steak knife, then called 911 to report “somebody with a knife breaking into the house.”

But cops said the wounded teen was able to finger her brother as the attacker.

The boy later told police his sister, who suffered stab wounds to her back, legs, thighs, arms and face, was “bothering him” before the attack, cops said.

One neighbor told The Post that the boy is autistic and is often heard having screaming fits.

“He screams a lot and there’s, you know, there’s a lot of yelling,” the neighbor, who declined to be identified, said. “They came here three years ago. Nicest neighbors we ever had. Never any trouble at all.”

“It’s terrible what happened,” he said. “My wife was really upset last night. The whole block was in shock. All the flashing red lights and the cops, and it was jus terrible.”