At least one person was in police custody and being questioned on Saturday in connection with the death of a 1-year-old boy who was apparently exposed to an opioid at a state-licensed Bronx day care center on Friday, according to the police.

Three other children were hospitalized after showing signs of opioid exposure at the day care, where the police later found a packaging device typically used by drug dealers, officials said. The New York City medical examiner’s office said an autopsy to determine the cause of death of the 1-year-old, whom the police identified as Nicholas Dominici, was scheduled for Saturday.

Joseph E. Kenny, the Police Department’s chief of detectives, said at a news briefing shortly after midnight on Saturday that the episode was the subject of an “active criminal investigation.” He added that suspicions about opioid exposure were prompted by the children’s symptoms and by the discovery of a so-called kilo press — commonly used by drug dealers when packaging large quantities of drugs — at the day care during the execution of a search warrant there.

The police did not name the person or people in custody on Saturday.

The day care, which the police identified as Divino Niño, is on a largely residential tree-lined block on Morris Avenue in the Bronx. According to public records, the day care at that location was registered in May and had capacity for eight children between 6 weeks and 12 years old.

Calls to a number listed for the day care were not immediately returned on Saturday. A woman who answered a phone for Grei F. Mendez De Ventura, a person listed as a contact for the location, said she did not wish to be interviewed.

Officials said the day care had been licensed by the state’s Office of Children and Family Services after passing two inspections. A “surprise” inspection last week by the city’s health department on behalf of the state agency found no violations, said Dr. Ashwin Vasan, commissioner of the city’s Department of Health and Mental Hygiene.

A spokesman with the state agency, Solomon Syed, said he could not comment on an active agency and law enforcement investigation.

According to officials, emergency medical workers responded to a 911 call requesting help for three unconscious children at the day care at 2707 Morris Avenue around 2:45 p.m. on Friday.

When they arrived, they found the 1-year-old boy, a 2-year-old boy and an 8-month-old girl unresponsive. The responders administered the overdose-reversal medication Narcan at the scene and took the children to Montefiore Medical Center.

The police later learned that another 2-year-old-boy, who had left the day care shortly after noon, had been taken to BronxCare Health System hospital after his mother noticed he was lethargic and unresponsive.

By early Saturday, three of the children had regained consciousness and were in critical or stable condition. The 1-year-old boy, who would have turned 2 in November, was pronounced dead at the hospital.

Claire Fahy contributed reporting.