The incident occurred at the daycare center in the borough of Queens at about 3:30 a.m. EDT, a spokesman for New York City Police Department said.
The unidentified worker stabbed two infant girls and one infant boy as well as a man, believed to be a father of one of the children, and a female coworker, police said.
One of the infants was in serious condition, the police spokesman said.
The suspect has self-inflicted wounds to the wrists and was in custody. She was in stable condition, police said.
Police said it was not immediately clear why she attacked the children and adults.