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SUITLAND, Md. — An 11-year-old girl has been charged in the death of a toddler she was left alone with while her own mother, who was watching the boy, ran an errand, police in Maryland announced Friday.

The children's families were friends and the mother of 1-year-old Paxton Davis of Washington, D.C., left him with the girl's family Saturday night, Prince George's County police said. The next morning, the girl's mother ran an errand, leaving the children alone at the Suitland home.

When family members returned, they found Paxton injured and called 911, police said. He was taken to a hospital with severe injuries to his upper body and hospital staff alerted police. The boy died on Thursday.

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The girl admitted to detectives that she assaulted the boy, causing injuries that led to his death, according to Prince George's County Police Maj. Brian Reilly, commander of the department's Criminal Investigation Division.

Paxton had been at the home before, but the girl had never cared for him before, Reilly said.

"It was an innocent, friendly agreement that obviously turned absolutely tragic," he said.

The girl, whose name was not released, has been charged with first-degree child abuse resulting in death and committed to a juvenile facility, police said.

Detectives spoke to the girl at length, but it's not clear why it happened, Reilly said.

"I don't have a motive for this. There's no words," he said. "There's no reason for this to take place."

Under Maryland law, a child cannot be left unattended without proper supervision by a reliable person at least 13 years of age. Police said in a statement that any further charges would be determined in consultation with the State's Attorney's Office.