The woman and her grandfather survived, but both her children were killed.
Two babies are dead, and a 70-year-old man and 20-year-old woman are in critical condition after an apparent murder-suicide attempt on Thursday.
Chicago police claim the woman stabbed her grandfather in the face and killed her eight-month-old son, leaving him in the bathtub. They said she then threw her two-year-old son out the 11th-story window before jumping out after him.
According to the Chicago Tribune, police were called to the 7200 block of South Shore Drive at 1:45AM on Thursday, where they found the woman and child on the ground.
They then made their way to the 11th floor of the 21-story building, where they found the man with cuts to his face and body, before they discovered the second boy, who had suffered scald and head wounds, unresponsive in the bathroom.
"The child in the bathtub appeared to be scalded from the water, and he had some lacerations on his head," Chicago police spokesman Anthony Guglielmi told the publication.
"Based on the positioning of the bodies and available evidence ... it appears as though the baby was thrown out of the window and the woman followed. We're assuming something broke her fall because she survived, which is unusual after falling from that distance."
The medical examiner's office has not yet confirmed the 8-month-old's cause of death. His brother's injuries were so extensive it was not yet possible to determine if he was killed before being tossed out the window.
"It's unclear if the other baby was also stabbed because of the trauma from the impact of the fall. We're not sure if he was stabbed or killed before he was thrown out the window," Guglielmi said.
According to police, the man told them his daughter "began stabbing him and then jumped from the 11th floor with her (2-year-old son)"; however detectives believe the woman is actually his granddaughter.
They have yet to formally interview either the man or the woman, nor establish a motive; however should she survive she will likely be charged, Guglielmi said.
"It is unclear, again, why she stabbed her grandfather. He was nearly stabbed to death," he said. "Hopefully, we'll get some answers, but we also may not, depending on how these individuals turn out."
"From what was described to me, it's just been a very difficult scene for detectives having to see children like this," he added. "It's hard for anybody — including cops and detectives — they're mothers and fathers too. For anybody to have to see a child lifeless in a bathtub is exceptionally difficult."