LAPD Sgt. Michael Mabie said Yaiza Cuevas went to a slumber party at a friend's house, and her mom was not aware of it.
The girl was reported missing by her mother on Friday after an apparent communication mix-up between the mom and the child's babysitter.
Cuevas normally gets picked up by her babysitter in the evening once she's done with after-school music classes at Logan Elementary School.
Friday, police said Cuevas told her babysitter, Rosa Caranza, that she didn't need to be picked up because she was getting a ride home from her mother's friend, Suzy Gonzalez.
The girl's mother, Mira Madrid, didn't know anything about that and reported her daughter missing to police.