The scene of horror happened on Hempstead Avenue in Midland Beach.
Police are still processing the scene, while the mother and her kids are listed in serious condition with multiple stab wounds.
When police arrived, they found the mother and her toddler in front of the residence with their throats slashed. She told police that her boyfriend had attacked them and then barricaded himself inside the house with her 3-year-old daughter.
"The cops had to break through to get in to get them out," neighbor Eddie Montanez said.
Police called in SWAT teams after 41-year-old Douglas Nemeth barricaded himself in the kitchen of the townhouse. Investigators believe he must have snapped, stabbing both 34-year-old Victoria Orlik and their 18-month-old son Brandon as she clutched the boy in her arms.
Then, he attacked their 3-year-old daughter Sasha and refused to come out.
Police stormed the house, and when they found them, they say he had stabbed Sasha in the neck and himself too.
All four were rushed to the hospital, where the father was pronounced dead.
Neighbors were stunned to learn about such an act of violence happening on their block.
"I didn't even know what was going on," Montanez said. "I came out to let my family out. I said what's going on, emergency? Let me get my family out of my house. They told me no, police emergency. They I found out it was a guy with a knife and he just stabbed everybody in the throat."