More drugs were found hidden under a trap door at the Bronx day-care center where a 1-year-old boy died last week after inhaling fentanyl, law-enforcement sources told The Post Thursday.

Investigators returned to the Morris Avenue apartment building in Kingsbridge about five days after little Nicholas Feliz Dominici was poisoned by the deadly synthetic opioid alongside three other toddlers at the day care – which was also a secret drug mill, authorities said.

Cops found a secret door in the kids’ play room Wednesday that led to a space with even more drugs, the sources said.

It’s not clear why cops went back to the home, or how many drugs they recovered from the scene.

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

The basement entrance in back of the building was closed Thursday morning, with a crime scene unit van and a police cruiser parked nearby and police tape blocking the door.

Two people — Grei Mendez De Ventura, the 36-year-old proprietor of Divino Niño Daycare; and her cousin-in-law, Carlisto Acevedo Brito, 41 — have been charged with murder for Nicholas’ death.

De Ventura’s husband – who cops have not publicly identified – is still on the lam.

The group allegedly used the business to cloak their true operation, a fentanyl drug mill.

The two people in custody also face federal drug charges for their alleged crimes, Manhattan federal prosecutors announced Tuesday.

Fentanyl — a powerful opioid that’s at least 50 times stronger than heroin — also sickened an 8-month-old girl and two 2-year-old boys, cops have said.

They were all hospitalized.

On Monday, Mayor Eric Adams said they were saved with naloxone, the overdose-reversal drug commonly known by its brand name, Narcan.

Little Nicholas, however, could not be saved.

His death has devastated his family.

“It’s really hard … we are all heartbroken,” the boy’s dad, Otoniel Feliz, said earlier this week outside the family home in Kingsbridge.

Feliz, who is a golf course maintenance worker in Westchester County, said his son had only been going to the day care for about a week before his tragic death.

“The drugs … this is dangerous,” he said. “My boy died. But it can be yours.”

In a Tuesday interview with The Post, the dad of one of the other victims said the drugged-up daycare center’s proprietors should be sent to prison.

“Those are bad people,” Jose Lino, 32, said as he cuddled his little boy, Jaziel, at their Bronx home.

Jaziel narrowly escaped death himself – his parents brought him to a Bronx hospital after they picked him up from the center and he couldn’t walk or wake up.

“They’re supposed to be taking care of little kids,” he said. “They’re not supposed to be doing that … in the same apartment.”