Police made an unexpected discovery while investigating an alleged fentanyl packaging operation hidden in a Williamsbridge apartment on Tuesday.

Officers say they disrupted the active drug mill inside a first-floor apartment at 755 East 216th Street.

Special Narcotics Prosecutor Bridget G. Brennan says the search quickly became a “rescue mission” as officers spotted Ariendy Jiminez-Hidalgo and her 2-year-old child inside a bedroom at the scene.

Prosecutors believe that five other children under the age of 15 lived inside the apartment as well, according to a press release.

Officials say the residence is also located near a public middle school, just across the street from a daycare center and playground.

The search recovered around four pounds of fentanyl mixtures with a street value over half a million dollars, along with tens of thousands of individual dose glassine envelopes.

Investigators also seized equipment such as grinders, cutting agents, masks and heat lamps.

Jiminez-Hidalgo, Jose Cordero-Concepcion and Erik Jesus Reynoso-Burgos were taken into police custody.

The charges against them include criminal possession of a controlled substance, endangering the welfare of a child, criminal use of drug paraphernalia, criminal facilitation and unlawfully dealing with a child.

Bail was set at $150,000 cash or bond for Concepcion and $50,000 cash or bond for Burgos. Hidalgo was ordered released on her own recognizance.