Heather Lynn Hess, 23, of the 1700 block of Hewes Avenue in Upper Chichester is charged with first degree murder in the death of two-year-old David Miller Jr.
Police say Hess was babysitting Miller at her home on the night of the December 11th when the boy went into respiratory arrest.
According to the affidavit, Hess told police that she found the boy unconscious and found a plastic bottle cap in his throat.
She told police she was able to dislodge the cap, but the boy still had trouble breathing and was bleeding.
Investigators say Hess called her boyfriend, then called 911 and started performing CPR. Medics took the boy to Crozer Chester Medical Center. He was then transferred to Children's Hospital, where he died the following day.
However, according to the affidavit, an autopsy performed by the medical examiner showed the boy died from blunt impact injuries to the head and ruled the death a homicide.
Investigators say the boy's body did not show any signs that he choked on a bottle cap.
The affidavit went on to say officers interviewed Hess again after the boy's death and, when police said the boy died of trauma to his head and brain, Hess reportedly said she couldn't explain how that happened.
Police arrested Hess on Friday night and she is being held without bail. She was charged with criminal homicide, first- and third-degree murder, aggravated assault, endangering the welfare of children and involuntary manslaughter.
Three other children, ages one through four, were also in the home that night, police say.