The death of a 2-year-old Bronx girl, which officials initially thought resulted from natural causes, turned suspicious yesterday when police arrested the girl’s mother and live-in boyfriend.

A law-enforcement official, who spoke anonymously because a final toxicology report is still forthcoming, said the urine of the dead toddler, Sherlyn Polonia, tested positive for cocaine. The autopsy prompted police to secure a warrant to search her family’s apartment on Bainbridge Avenue in Kingsbridge, where they said they found more than four ounces of cocaine and drug paraphernalia in the bedroom where the child slept. They arrested the girl’s mother, Johanna Bare, 23, and her live-in boyfriend, Johnny Carvajal, 47, charging both with drug possession, reckless endangerment, and endangering the welfare of a child.

According to police, Mr. Carvajal has two prior arrests for misdemeanor drug possession, with the most recent in March of last year. Neighbors in the Bronx, speaking through a translator, said they didn’t know the family well. Despite the likelihood that the child ingested such a large amount of cocaine in her own home, neighbors said they noticed nothing about the couple that seemed out of the ordinary. According to the building’s superintendent, Ms. Bare had lived in the building for around a year, while Mr. Carvajal moved in six months ago. A neighbor, Martha Arias, who lives down the hall from the couple, said she saw Ms. Bare taking another child to school a few times. According to police, that 6-year-old boy was placed in the custody of the New York City Administration for Child Services.

Police had initially responded around 8:50 a.m. on Wednesday to a 911 call placed by a relative from the family’s fourth-floor apartment. According to police, the toddler was found on a couch and not breathing. Emergency Medial Service personnel performed CPR and brought the girl to Montefiore Hospital, where she was pronounced dead at 9:25 a.m. Yesterday, a spokeswoman for the medical examiner said an autopsy had been performed, but the investigation would not be completed until the middle of next week, pending the results of further toxicology tests.

A spokeswoman for the Administration for Children’s Services said yesterday that the agency did not have a history of involvement with the family of Sherlyn Polonia. Other recent cases of violence against children in the city include the death of seven-year-old Nixzmary Brown on January 11 and the alleged attempt to drown 5-month-old Elizabeth Gonzalez earlier this week.