The toy bills were Chinese joss paper, or "spirit money," that had been distributed at a local festival earlier this year, and resembled crude euro bills. (Switzerland's currency is the Swiss franc.)
According to an account by the boy's family, the children forgot about the encounter until weeks later, when the local police arrived.
Following internal rules that require employees at the supermarket chain the children visited to report suspected counterfeit payments, the cashier had alerted police, who examined the store's security footage.
A police officer called the boy's family May 28 to inform them that he would visit and told the boy's mother that he was investigating an "official offense," according to the family.
Instead of ending with a metaphorical slap on the wrist, it resulted in a police visit to the family home, an upcoming appointment at social services and a distressed 8-year-old asking his mother whether he would be going to jail, the family said. The police officer confiscated more toy bank notes during the visit and took mug shots of the two brothers.
The children's identities have not been disclosed by the police or the Swiss news media to protect their privacy.
A spokesman for the regional police said in a statement that the officer had come to clarify whether the counterfeit money was being used deliberately and whether the children's act was punishable by law.
Under Swiss law, children younger than 10 do not face penalties. The police spokesman said the officer had taken pictures to prove that the 8-year-old boy, and not his 10-year-old brother, had presented the fake bill.
"In retrospect, it was not absolutely necessary for the children to be photographed," the spokesman added.
The police also said there had been a second incident later the same day in which the children returned to the store, but the police would not provide details "for reasons of personal protection." The family denied that there had been a second incident.
Facing fallout in the local parliament in Basel-Landschaft on Thursday, Kathrin Schweizer, the government official who oversees the police department, maintained that while the photos were not necessary, the police had acted properly.
The supermarket chain, Volg, said in a statement that although the employee had followed instructions, a "different response would have been desirable" because of the children's age.
"We tried to talk to the affected family and apologised in all forms," said Tamara Scheibli, a spokeswoman for Volg.
In the comments section of the Basler Zeitung, a regional newspaper that first reported the story, dozens of readers commented on the absurdity of the situation and said the police should have apologised.
One reader's response, "Just burned my Monopoly game just to be on the safe side."
Written by: Elian Peltier and Christopher F. Schuetze
© 2020 THE NEW YORK TIMES