The mother was still recovering from her wounds in a hospital Friday evening. The boy's father was in custody.
The stabbing took place about 11:00 a.m. Friday in the 5000-block of W. Division.
The police have the suspect in custody. Witnesses say he was in a relationship with the woman and was the father of the boy who was killed.
Neighbors heard screams coming from the second-floor apartment about 11 o'clock. They then watched Margaret Jefferson jump from her apartment window, her arms bleeding, apparently from the suspect's attacks with a kitchen knife. Her cousin, Leslie Scott, was one of the first people she saw on the sidewalk outside.
"She was bleeding out the arms and she ran to me and hugged me and said... [he's] got Jaivon up there and he says he's gonna kill him," said Scott.
Jefferson was trying to get help as her 3-year-old son was still upstairs with the suspect, his father. By the time police arrived, the boy had already been stabbed several times. Jaivon Sandifer died a short time later.
"I just can't imagine why a father - anybody would harm a child under any circumstance anywhere, because they're kids," said neighbor Dana Williams. "It's a tragedy, it's crazy, man."
"I just helped them bring in their groceries last night - J-Man included," said neighbor Cornelius Bussell. "J-Man wanted to carry in the watermelon. I tried to let him carry it, little guy, you know, and now this morning - he's gone."
The suspect jumped out of the back balcony of the apartment, apparently injuring himself in the fall. Police found him in a neighbor's garage and took him into custody.
"[Jaivon] was just a sweet boy - his grandmother and grandfather, they adored him, and they just loved him," said Scott. "His grandmother is going to be devastated."
Neighbors said the suspect has a history of domestic violence issues with the mother. Several of her friends say they urged her to get away from him. Jefferson was in stable condition at Stroger hospital Friday night with injuries that are not considered life-threatening.
No charges had been filed Friday night.