NEW YORK — A 4-year-old boy and his grandmother who died in Brooklyn last year were poisoned — and police are investigating both of their deaths as homicides, the NYPD said Thursday. 

Tofoon Man, 63, of the Lower East Side, was at her grandson Wilhelm Ducatl’s home in Mapleton last February when she started to experience stomach pain, police said. 

Man was taken to Mount Sinai Brooklyn, where she was pronounced dead on Feb. 17 of last year, the NYPD said. 

Three months later, on May 24 of last year, emergency personnel responding to a 911 call transported Man’s grandson to Maimonides Medical Center in critical condition after he began to feel stomach pain inside his home, police said. 

The boy was pronounced dead two days later, the NYPD said. A preliminary probe found that he might have been poisoned, “prompting further investigation” into his grandmother’s death, according to police.

Investigators exhumed Man’s body, and the city’s Office of Chief Medical Examiner on Wednesday said both Man and her grandson died of acute thallium poisoning. 

Police sources told NY1 the boy’s parents had been in a custody dispute at the time of his death, but no one had been arrested in connection with either death as of Wednesday. 

It wasn’t immediately clear how the two were poisoned. An investigation is ongoing.