NEW YORK (Reuters) - The New York woman who discovered her children’s bloody bodies in a bathtub and their nanny stabbing herself in the neck testified on Thursday at the start of the babysitter’s murder trial that the experience was a “nightmare.”

After opening statements in which the prosecution described the grisly killings and the defense urged jurors to find the nanny, Yoselyn Ortega, not guilty by reason of insanity, the mother of the slain children appeared as the first witness.

Marina Krim recounted going home to her luxury apartment on Manhattan’s Upper West Side on Oct. 25, 2012, only to discover her daughter Lucia, 6, nicknamed Lulu, and son Leo, 2, stabbed to death.

“I just wanted to wake up from this nightmare that I knew wasn’t a nightmare. It was real,” Krim told the jury, often sobbing on the witness stand in state Supreme Court in Manhattan.

Ortega, 55, on trial for two counts of first-degree murder and two counts of second-degree murder, planned the killing, waiting to be alone with the children and using the family’s kitchen knives, said Assistant Manhattan District Attorney Courtney Groves.

Lucia, who fought back, had 20 to 30 stab wounds, Leo had five gashes, Groves said.

Ortega waited to stab herself in front of Krim so she could see her reaction, the prosecutor said.

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The petite, bespectacled nanny had been hired two years earlier by Krim and her husband, then-CNBC executive Kevin Krim.

Ortega resented Krim for being the mother “she could never be,” Groves said.

Ortega had recently brought her son, Jesus, 17, from the Dominican Republic, enrolled him in a private school so he did not have to repeat 11th grade, and was overwhelmed by financial concerns. Ortega was “enraged” that Marina Krim offered to find her more work, Groves said.

Before the trial adjourned for the day, Krim testified she had clashed with Ortega in the past over an offer by a friend of the Krim family to hire her as a household helper. Few details were disclosed, but Krim testified that the following day she confronted Ortega.

On the day of the murders, Krim had returned home with her third child, then 3-year-old Nessie, after Ortega failed to appear with the other children at a designated meeting place.

She rushed inside and started checking every room, thinking, “it’s like a total horror movie,” Krim testified.

Seeing blood drenching the bathroom, she ran out of the apartment screaming, she testified, adding, “It was a scream you can’t even imagine is inside of you.”