A mom weeps for her two murdered children, and the nation weeps with her.
Doctor Marina Krim returned home to find her son and daughter stabbed to death, allegedly by the nanny.
Videos of the little victims posted online will break one's heart.
Cops say the mom was at a swimming lesson with her third child when she returned to her apartment building known as La Rochelle. She found the apartment in darkness. When she searched the apartment, she found the two children in the bathtub. Neighbors heard her screaming, "My babies, my babies!"
One neighbor told INSIDE EDITION, "I heard a female screaming, just screaming blood-curdling screams. The sounds I could make out was,'So you cut her throat? You stabbed her and cut her throat?!' "
Little Lulu and her brother Leo were rushed to the hospital but could not be saved. Cops say the nanny, identified as Yoselyn Ortega, tried to kill herself but survived.
New York City Police Comissioner Ray Kelly said at a press conference, "On the floor of the bathroom is the nanny, who apparently had inflicted wounds on her throat."
Dr. Krim was covered with a sheet as she was escorted by police to be treated for trauma. Three-year-old Nessie, her only surviving child, was seen peaking out from the sheet.
The killings took place in one of New York City's most exclusive neighborhoods, just off Central Park. As a shrine grew outside the building, other moms in the area reacted with horror and tears.
One area mother tearfully said, "It hits really close to home. It's unimaginable. It's a tragedy and I feel so terrible for this family."
"It's unimaginable. There's no words to describe what they're going through. And we all came together for support because there's obviously nothing that any of us can do," said another neighbor.
Another area mother was too upset to even speak.
Dr. Krim is a pediatrician who had given up her career to be a stay-at-home mom. Her husband, Kevin, is a senior executive for CNBC TV. He graduated from Harvard. He was returning from a business trip on the West Coast when the tragedy happened. Cops met him at the airport and told him of the grim news.
In the wake of the tragedy, mothers everywhere are taking extra precautions. INSIDE EDITION spoke to security expert Pat Brosnan.
"You have to know what their history is. You're bringing them into your home and handing them one child, two children, the keys to the crib, the keys to your house," said Brosnan.
By all accounts, the Krims did everything they could to check out their nanny. When they vacationed recently in the Dominican Republic, they even spent time with the nanny's family to make sure she was suitable.
At The Spy Shop in New York, worried parents are calling non-stop.
Parenting expert Lyss Stern told INSIDE EDITION, "My emails, my Facebook posts, worried moms, hundreds of them have been emailing and calling me about where they can find a nanny cam."
Now, America's heart goes out to the grieving parents and their surviving daughter, Nessie. Nessie must now grow up without her sister and brother.