A newly released audio recording recounts the harrowing events at a Florida apartment last week, where a 40-year-old Philadelphia woman allegedly killed her two young children while visiting family.

In the 911 call, posted online by the Miami Herald, Sophia Hines' cousin can be heard describing a chilling scene to dispatchers: "There's 2 babies on the bed, not breathing," she says, telling the emergency line she thinks the children are dead.

Hines, of Philadelphia's Frankford section, was charged with two counts of premeditated murder in the deaths of her 7-month-old son and 3-year-old daughter. Court documents say she admitted to suffocating the children with a bedsheet while visiting her cousin in Miramar, near Fort Lauderdale.

In the eight-minute 911 call, the cousin tells dispatchers that Hines told her to return home, saying something was wrong at the house. When she arrived, the cousin saw the children unresponsive on the bed, with "blood coming from the little girl's mouth and her nose."

The cousin also told 911 she was frightened: "I don't know what she did and I'm not going to stay in the house by myself with her."

Hines offered no motive for her alleged actions, court documents say.

She was being held without bond. Her defense attorney told the CBS affiliate in Miami that her client was suffering from severe post-partum depression.