Yoselyn Ortega was formally charged with first-and second-degree murder Saturday night after investigators interviewed the 50-year-old from her hospital bed.
Officers say on Oct. 25, Ortega fatally stabbed 6-year-old Lucia Krim and her 2-year-old brother, Leo, before stabbing herself.
A third sibling was with the mother when she discovered her children in the bathtub and Ortega on the bathroom floor of the family's apartment. A kitchen knife was nearby.
The children's father, CNBC digital media executive Kevin Krim, had been away on a business trip when the killings occurred.
Some of Ortega's friends and relatives said she appeared to be struggling emotionally and financially recently, but they still couldn't believe she could have committed such a heinous act.
It is unknown if Ortega has a lawyer.
The Associated Press contributed to this report.