Updated

A New York City mom walked into her home Thursday to find her two small children stabbed to death in a bathtub, police say, while the nanny watching over them was seen sitting in a pool of blood with a kitchen knife nearby.

The 2-year-old and 6-year-old children were found dead in the apartment at a building called La Rochelleon on Manhattan's Upper West Side. It's unclear how many times they were stabbed.

Police Commissioner Raymond Kelly said the mother arrived at the dark apartment near Central Park on Thursday evening and initially thought the nanny had taken the children out.

Cops found the nanny on the floor of the bathroom and said she had stab wounds believed to be self-inflicted. Sources told the New York Post that she slit her wrists in a failed suicide attempt.

“Something happened to my kids!” the sobbing mother screamed, according to witnesses who spoke to the newspaper.

Neighbor Rima Starr said she heard someone screaming, "You slit her throat!"

The mother called 911.

Both children were rushed to St. Luke's-Roosevelt Hospital Center but were pronounced dead on arrival. The mother, taken to the same location, had to be sedated, a source told the New York Post.

The nanny is hospitalized in critical condition and is in police custody.

Click for more from the New York Post.

The Associated Press contributed to this report.