The two girls, who are cousins, are suspected of robbing a hamburger store in Halmstad, southern Sweden, in late March. During the robbery, the thieves had a large kitchen knife that they used to threaten the staff at the restaurant.
"Give me the money otherwise I'll stab you," they said, according to the restaurant chef account of the robbery, wrote the Aftonbladet newspaper.
"Calm down, I'll open the till," he responded.
The pair managed to get away with 2,420 kronor ($370), but were traced by police sniffer dogs back to their grandparents' apartment, outside which a bag was found with the knife and balaclavas. The girls were arrested on the scene.
During the arrest, officers confiscated a phone on which they found pictures of the duo before the robbery wearing the balaclavas and holding the knife.
While the younger of the two girls is too young to be charged, her 17-year-old accomplice will stand trial on August 2nd. The seized pictures will be used as evidence against the teen, as will DNA traces taken from her balaclava.