Yoselyn Ortega entered her plea through her attorney while handcuffed to her hospital bed. She's being treated for self-inflicted stab wounds. The 50-year-old appeared alert but didn't speak during the Wednesday hearing.
Ortega is being held without bail while she undergoes a psychiatric exam.
Last month, Marina Krim returned to her home to discover her 6-year-old daughter and 2-year-old son dead of knife wounds in the bathtub. Ortega was found lying on the bathroom floor with stab wounds to her neck. A kitchen knife was nearby.
Both parents are originally from Southern California. Marina Krim grew up in Manhattan Beach and her husband Kevin is from Thousand Oaks. Kevin Krim, a CNBC digital media executive, was away on a business trip when the killings occurred.
The Associated Press contributed to this report.