“Antonio was shot in the mouth, and the bullet went through the back of his head,” his uncle, Manuel Samuel, told the BBC.
“We saw CCTV footage from nearby shops of police shooting at protesters,” he added.
Antonio Juaqim’s killing is a tragic reminder of the volatile political climate in the southern African state since Frelimo – the former liberation movement in power since independence 49 years ago – was declared the winner of the poll.
The electoral commission said Frelimo’s presidential candidate, Daniel Chapo, won with a whopping 71% of the vote, compared to the 20% of his closest rival, Venâncio Mondlane.
An evangelical pastor who contested the presidency as an independent after breaking away from the main opposition Renamo party, Mondlane rejected the declaration, alleging the poll was rigged.
This was denied by the electoral commission, but Mondlane – who fled the country, fearing arrest – has rallied his supporters via social media to protest against the result.
Every night at 21:00 local time (19:00 GMT), people have been banging pots and pans in their homes, as they heed Mondlane’s call to send a loud message that they reject an extension of Frelimo’s 49-year rule.
Samuel said the protest was first held on the night of 15 November when huge numbers of people took to the streets to bang pots, pans and bottles or to blow whistles.
“It was as though a new Mozambique was being born,” he added.
But the night ended tragically, with Antonio being among those killed by police, Samuel said.
Since then, most people have been carrying out the protest inside their homes, with the sound of banged pots and pans echoing across Maputo at 21:00 every night.
At Antonio’s funeral at the São Francisco Xavier Cemetery four days after his killing, one of his friends delivered his mother’s eulogy: “You were so full of life and hope. Now you are a victim of a bullet.”
Crying, Antonio’s friends planted flowers on his grave before bursting colourful balloons over it, a reminder that he was just a child.
“At the morgue, I counted six bodies of young children,” Manuel told the BBC.
“They are killing us and our future,” he added.
Campaign group Human Rights Watch said that about 40 people – including at least 10 children – have been killed by police during the post-election protests.
Mozambique’s police commander Bernadino Raphael expressed sympathy with the families of the victims, but deflected responsibility for the deaths, blaming Mondlane’s supporters.
“They are using children as shields in front of them while they remain behind,” he alleged in a BBC interview.
The commander added that in many instances police had no choice but to defend themselves from protesters who had unleashed violence, including killing six officers and looting and burning property and vehicles.
“We recorded 103 injured people, 69 of whom were police officers,” he said.