Officers were shown bundling the screaming boy into a police car in central Moscow as he shouted "Save me!" in distressing cell phone footage aired on Russian television.
Police claimed the boy, named by media as Oskar Mironov, had been "begging" on the street on Friday evening. They held him at a police station until the early hours.
The boy's father told Russian media his son had been reading poetry aloud while his stepmother sat on a bench nearby.
The Investigative Committee of Moscow, which probes serious crimes, said it would check the police's handling and the parents' actions. Moscow police said they were also carrying out a check and would "make public" the result.
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Days before a journalist at Moskovsky Komsomolets popular daily had praised the boy for his street poetry reading, posting a Facebook video.
The slight boy in glasses is shown reading by heart the Hamlet "To be or not to be" monologue on Arbat, a popular pedestrian area.
He said passersby gave the boy small amounts of money but he was not begging.
OVD.Info website, which monitors detentions, said the boy and his stepmother spent around four hours at the police station, leaving after midnight.
The boy's stepmother shot cell phone footage as the police took away the boy and told Russian media she followed him to the station. It was unclear why the incident escalated.
The boy's father told Life News media group that his son had been practising his acting skills.
It is unusual to see children performing on Moscow streets and busking is not universally accepted. Moscow metro only recently lifted its ban on musicians.
Police however said they had charged the boy's father with failing to carry out his parental duties, carrying a fine of 500 rubles (USD 9).
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