Ortega stabbed and slashed the children in the rear bathroom of the second-floor apartment of the La Rochelle before plunging a kitchen knife into her own throat in a failed suicide attempt.
In sentencing Yoselyn Ortega, fifty six, the judge described her "pure evil" ahead of devoting her utmost term.
It provided a much-needed measure of relief for the parents of 6-year-old Lulu and 2-year-old Leo Krim, who were savagely slain in the bathroom of their Upper West Side home on October 25, 2012, while the mom was at a swim class with their middle sibling Nessie, then 3.
The children's distraught mother lashed out at Ortega for not showing "an ounce of remorse" and for plotting to "destroy" her family.
The case hinged on evidence presented about Ms. Ortega's mental health history and her state of mind at the time of the slayings, much of which countered her argument that she was in the grip of severe psychosis. "Nessie knows this wish will never come true". I just thought: 'I'm never going to be able to talk to them ever again.
On the day of the murders, the children's mother, Marina Krim, arrived back at their Upper West Side apartment with her third child to find Lucia and Leo dead in her blood-soaked bathroom. Ortega had been recommended by her sister, a nanny for another NY family, and her background and references were faked by her family. "It was real", Krim told jurors.
"It is so unfair that they are gone, unfair to us, unfair to the world", said Mr Krim.More news: F1: Hamilton clinches pole position for Spanish GP
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Both Marina and Kevin Krim each read their own victim impact statements in court, recounting memories of their children taken from them.
"My client is severely ill, she is psychotic", Valerie Van Leer-Greenberg said, appealing for her to be placed in protective custody.
On Monday, Ortega appeared visibly shaken as she apologised even though covering the courtroom.
"I ask for a great deal of forgiveness - to God, to Marina, to Kevin", she said, wearing an oatmeal top and her dark hair scraped back into a ponytail.
Jurors and members of the audience also wept up when Kevin and Marina - the first and last witnesses on the prosecution's direct case - took the witness stand.
Vance yawned as Ortega's lawyer, Valerie Van-Leer Greenberg, claimed that the jury was swayed exclusively by emotion.
Prosecutors say Ortega knew what she was doing and understood "each stab, each slash" as she slaughtered the youngsters.