A woman stabbed her seven-year-old son 100 times and a five-year-old girl about 50 times and slit both their throats because she was angry with her husband, prosecutors have said.
Elzbieta Plackowska, 40, is accused of killing her son and a girl she was babysitting in Naperville, Illinois, on Tuesday.
A judge has now ordered that she should be held without bail.
DuPage Country Prosecutor Robert Berlin said Plackowska had admitted she killed her son, Justin, because she was upset that her truck-driver husband had left her alone to care for him.
"She told the detectives that she thought by killing Justin she would make her husband hurt the way she hurt in their relationship," Mr Berlin said.
He added: "She had grabbed a knife and she made both victims kneel and begin praying. She began stabbing her son Justin and told him he was going to heaven tonight. He pleaded for his life and told her to stop. But she continued stabbing him until he was dead."
Plackowska reportedly told authorities she killed the girl, Olivia Dworakowski, because she had witnessed the first murder.
The attacks began when she found the children jumping on a bed, Mr Berlin said.
Plackowska initially told police a stalker had broken into her home and killed the children, before admitting to her actions.
She did not speak during the hearing aside from indicating she could not afford an attorney.