Yoselyn Ortega, 55, is charged with murdering 6-year-old Lucia Krim and 2-year-old Leo Krim in their Upper West Side home in 2012.
Prosecutors say she killed the siblings in response to an argument she had with their mother.
Her attorney is expected to use an insanity defense.
Ortega faces a possible sentence of life behind bars. She is currently being held without bail.
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