Tucson Police Department spokesman Sgt. Chris Widmer said the girls, ages 9 and 11, were arrested Sunday after one called from a cellphone, claimed to be Isabel Celis and that she'd been kidnapped, then hung up, the Tucson Arizona Daily Star reported Monday.
Celis, 6, was reported missing by her father, Sergio Celis, from their home April 21. She has not been found.
After receiving the call, Widmer said, police canvassed the neighborhood looking for the caller, leading to an apartment complex.
Police said the sisters admitted to making the 911 phone call as a prank, the Daily Star said. The girls' mother was home, but was unaware of the telephone call.
Police arrested the sisters on suspicion of false reporting to a law enforcement agency, and took them to Pima County Juvenile Detention Center. They weren't held because they didn't meet the juvenile court's criteria for detention, Stephen Rubin, the juvenile court's administrator, said.
Rubin said the Pima County Attorney's Office would decide whether the girls would be charged.