The father of the 1-year-old boy killed by fentanyl at a Bronx day care that allegedly served as a front for a drug mill said Thursday the family had “trusted” the center’s owner – as she was indicted on murder charges along with her husband and his cousin.

Otoniel Feliz, dad of tragic tot Nicholas Feliz Dominici, said that during the brief period his son was enrolled at the Divino Niño Daycare in Kingsbridge, owner Grei Mendez, 36, would regularly send his wife text updates of “each and every little thing.”

“We trusted her,” Feliz said of Mendez following her arraignment in Bronx Supreme Court.

“We feel betrayed by that day care,” Feliz continued, holding up a photo of his late son, adding he had hoped to one day have a graduation picture of the boy – but now all he has “is a reminder of his death.”

Little Nicholas was at the day care on Sept. 15 when he died, in what the city medical examiner’s office has ruled a homicide by acute fentanyl intoxication.

“We feel really emotional because we remember every single detail from this tragic event. It’s really hard for us,” Feliz said during a press conference at the Bronx District Attorney’s Office.

Mendez — along with husband Felix Herrera Garcia, 34, of the Bronx; and Carlisto Brito, 41, also of the Bronx — was indicted Thursday on charges of second-degree murder, second-degree manslaughter, assault and drug possession, among others.

All three defendants each pleaded not guilty, with Brito telling Acting Bronx County Supreme Court Justice Margaret Clancy in Spanish, “No culpable.”

The trial will likely start Dec. 19.

Authorities say the trio ran a fentanyl mill out of the building’s basement. This led to four children — including the now-deceased Nichols – being sickened after they were exposed to the deadly synthetic opioid, which is about 50 to 100 times stronger than heroin.

The wannabe drug lords allegedly stored the fentanyl under two trap doors inside the day care center and in closets on top of the play mats.

“This was not really a day care center — this was a drug operation,” Bronx District Attorney Darcel Clark said at the press conference. “And they used babies as a shield. I’m outraged.”

The three other children — an 8-month-old girl, her 2-year-old brother and another 2-year-old boy — had to be revived using naloxone, the overdose-reversal drug commonly known by its brand name of Narcan.

Authorities arrested Mendez and Brito — who is Herrera’s cousin — the day after Nicholas’ death and charged them with murder, assault and child endangerment.

Herrera, 38, was nabbed on a bus by Mexican authorities last week after 10 days on the run.

Herrera, Mendez and Brito also face federal drug charges related to Nicholas’ death.

A fourth defendant, 38-year-old Renny Antonio Parra Parades, was also charged by Manhattan federal prosecutors for his role in the alleged drug operation. 

Herrera — described as “the main player” in the alleged drug business — is no stranger to overdose deaths.

Last year, a man he allegedly identified as his brother OD’d and died, law enforcement sources previously told The Post previously.

Authorities initially said they uncovered a kilo of fentanyl sitting on mats the children slept on, according to court papers. They also seized several “kilo presses,” which are usually used to combine the drug with cocaine or heroin.

A week later, more drugs were found hidden under a trap door at the day care center, including six kilos of fentanyl, heroin and other controlled substances, authorities said.

The stash was discovered in a 4-inch-deep hiding spot below the apartment’s tile-on-wood flooring, according to photos shared by the department.

Clark, the district attorney, said the case is the “bleakest reminder” that authorities must be “relentless in removing drug traffickers from our city and our borough.”

“For years, our community here in the Bronx has been the hub for fentanyl distribution, and has suffered so many deaths,” he said.

But for Feliz, the heartbroken father, the damage is already done.

“Nothing will bring him back.”