A woman has been accused of killing her own grandson after rubbing the drug methadone into his gums to make him sleep.

Towanda Reaves, 50, has been charged with murder and child abuse, and also injected the 17-month-old's sister, who survived the dose.

"She confirmed that she had given methadone to the children and put it on the gum lines of their mouths," Detective Jeremy Silbert of Baltimore City Police, told the local TV channel.

Emergency services were called to the Franklintown area of Baltimore just before dawn on 4 July. Paramedics attempted to resuscitate the boy but were unable to save him.

Reaves told investigators she put her grandchildren to sleep around 8pm, according to reports. She said she could still hear them breathing when she woke up around 2am to turn off the air conditoner, but one of the toddlers was unresponsive by 4am, and she called 911.

At the time, the boy's father was asleep on a sofa, she said.

Aadyn Overton was pronounced dead at a local hospital less than an hour later, reported ABC2.

On 5 July, the boy's sister, who is two months younger, was admitted to the intensive care unit at the hospital, and tested positive for methadone.

Detectives said Reaves had handed in an empty bottle of the drug, which is an analgesic used to treat heroin addicts, and admitted she had given it to the children.

The girl is expected to make a full recovery.

Last Wednesday, the chief medical examiner listed methadone intoxication as the cause of the boy's death.

Police charged Reaves with second-degree murder, child abuse resulting in death, assault, child abuse causing serious injury and reckless endangerment on 1 August.