NEW YORK, United States -- A New York woman is facing murder and drug charges after a one-year-old boy died from fentanyl poisoning at the daycare she operated and three other children became seriously ill, officials said Tuesday.

Grei Mendez, 36, was arrested over the weekend after emergency paramedics responded on Friday to reports of unconscious children at the Divino Nino Daycare in the Bronx.

Police said a large quantity of fentanyl was found at the facility, including a kilogram of the drug stored on top of children's playmats.

Four children under the age of three were hospitalized and one of them died.

Mendez and Carlisto Acevedo Brito, 41, a tenant in the apartment where the daycare was located, face New York state charges of murder, drug possession and intent to distribute.

They were slapped with federal narcotics charges in an additional indictment unsealed on Tuesday.

"Tragedy doesn't begin to describe the events that took place at Divino Nino Daycare," Drug Enforcement Administration special agent Frank Tarentino said in a statement.

"This death and drug poisonings are every parent's worst nightmare and clearly define the danger fentanyl poses to every New Yorker," Tarentino said.

US Attorney Damian Williams said Mendez put children "directly in harm's way, running a narcotics operation and storing deadly fentanyl out of the very space in which the children ate, slept and played."