Police say the 27-year-old mother, Chanthy Mao, took a kitchen knife, walked into her children's bedroom, and stabbed her 12-year-old daughter and her 8-year-old son to death.
"It just goes to the heart and hurts to see that such tragedy has struck," South Philadelphia resident Clifton Silver said.
It was around 5:30 p.m. when officers were called to the 1700 block of South 18th Street. When they arrived, they found the two children with multiple stab wounds to their chests.
Chea Meas, a family friend, says Mao was a good mother to her kids.
"It's unbelievable, the mother seemed to be okay and killed her children, it's kind of strange," Meas said. Neighbors say Mao was covered in blood when paramedics took her out on a stretcher and took her to the Hospital of the University of Pennsylvania.
"They believe they she may have been under the influence of something based on the bizarre behavior she was displaying," Philadelphia Police Chief Inspector Scott Small said.
Small says, at this point, investigators do not know what made Mao snap and commit such an unthinkable crime.
"It's a terrible thing for anyone to fully comprehend and understand," Small said.
Action News has learned that Mao, who is from Cambodia, moved to Philadelphia with her children more than a year ago.
The family had recently moved into the South Philadelphia home with the mother's parents.
Neighbors say the stepfather of the children rushed to the scene and had an emotional breakdown in the middle of the street.
"It is mind-boggling. You see things like this on the news, but you don't ever to expect to see it in your neighborhood. It only goes to show you people are just sick everywhere," Happy Terry of South Philadelphia said.
The grandmother and other family members arrived to the scene after the stabbings. They were taken to police headquarters for questioning.