The child triggered concern when he refused to take part in a minute's silence at his school in the southern city of Nice after Islamist gunmen shot dead 12 people at the Paris offices of the satirical weekly Charlie Hebdo on January 7, according to Marcel Authier, in charge of the region's public security.
The boy's teacher said the child also expressed "solidarity" with the gunmen.
"In the current context, the principal of the school decided to report to police what had happened," said Authier, who stressed no complaint had been filed against the boy.
"We summoned the child and his father to try and comprehend how an eight-year-old boy could hold such radical ideas," he added.
"Obviously, the child doesn't understand what he's saying," he said.
The boy's lawyer Sefen Guez Guez was not immediately available for comment but on his Twitter feed (@IbnSalah) he wrote that the child admitted to police saying the words: "I am with the terrorists".
Yet when police asked what the word "terrorism" meant, he replied: "I don't know", according to the tweet.
"Father and son are deeply shocked by their treatment which illustrates the collective hysteria that has engulfed France since early January," said the Collective Against Islamophobia in France (CCIF) in a statement.
The Charlie Hebdo murders kicked off three days of Islamist attacks in Paris that left 17 people dead and traumatised the country.

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