Liliana Carrillo, 30, was the sole suspect in the death, LAPD officials said at a news conference.
The babies are 3, 2 and 6 months old, said Lt. Anthony Kato.
A law enforcement source told CNN the three were stabbed. The police have not yet reported the cause of death.
There were no immediate police reports and it was not known if Carrillo had a lawyer.
The suspect’s mother found a child in the neighborhood of Reseda, said Lt. Raul Javel.
The officials did not cite the possible motives.