Two Tennessee grandparents have been charged with first-degree murder after their 20-month-old grandson died of a fentanyl intoxication.

There was “enough fentanyl in his system to kill an adult,” Metropolitan Nashville Police Department said in a news release.

Charles Allen Sr., 80, and Yolanda Newsome, 58, from East Nashville, were arrested on Thursday, March 3, and charged with first-degree murder, according to police.

Allen and Newsome were taking care of Korran Newsome, their 20-month-old grandson, on Aug. 6 while his mother was working. The grandparents had Korran in bed with them that night.

When Korran’s mother came home from work, Korran was not breathing, police said.

CPR was done, and the toddler was immediately taken to a local hospital.

He was pronounced dead briefly after his arrival, authorities said.

Police said his body had no signs of abuse or trauma. A medical examiner ruled the cause of death as “acute fentanyl intoxication.”

The grandparents both said they bought heroin off the street, and police said they allowed “Korran to be exposed to heroin containing fentanyl while in their care, specifically in their bed.”

A judge set bond for Newsome at $100,000 and for Allen at $150,000, authorities said.