The boy was killed in Woolwich, southeast London, the Metropolitan Police said.
Two teenage boys, aged 14 and 16, as well as an 18-year-old man were arrested on suspicion of murder on Thursday and are still being held in custody.
Police had previously referred to the victim as a man because they could not identify him but have now confirmed he was 14 years old.
Detective Chief Inspector Lucie Card, who is leading the investigation, said: "Our thoughts remain with the boy's family and loved ones.
"We are aware of the concern that this incident will cause the local community. We have already made three arrests and our investigation continues at pace. An increased police presence remains in the area.
"I would appeal for anyone who was in the area at the time, who has CCTV or dash cam footage of the incident or has information that could help my officers to come forward."
Officers were called to the scene in Lord Warwick Street, which is close to the Woolwich Ferry and Woolwich Dockyard train station, at around 3.40pm on Thursday.
The boy was pronounced dead at the scene and police said his family are being supported by specialist officers.
It is the second fatal shooting in the capital in less than a week.
Nahom Medhanie, 26 was shot dead in while sitting in a car near Euston station in central London at around 11pm on Saturday.
Retail director Thinus Keeve hit out at the government and London mayor Sadiq Khan in a letter posted to the supermarket's website.
"Without a government seriously cracking down on crime and a mayor that prioritises effective policing, we are powerless," he said.
Following unrest on Saturday, about 100 officers responded to antisocial behaviour in Clapham, south London, on Tuesday, four of whom were assaulted, along with one member of the public.
Scores of teenagers and young adults were participating in so-called "link-ups" – using social media apps including TikTok and Snapchat before surging into shops.
M&S was reportedly one of the stores targeted.
Mr Keeve went on: "It is becoming more brazen, more organised and more aggressive."
"We need a stronger, faster and more consistent police response, using tools that already exist to target repeat offenders and crime hotspots," he said, adding: "It's a clear ask: support our police. Help them show up in our communities when and where we need them.
"Give them the resources they need to tackle crime effectively, and ensure they work with retailers to consistently use the tools we've developed to share data and actively target offenders."
'None of us believe crime is falling'
He also questioned claims that crime rates are falling in the capital.
He said: "I keep hearing crime is falling, especially in London - something none of us believe, and very few people working in retail would see."
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M&S chief executive Stuart Machin has written to the Home Secretary Shabana Mahmood following the scenes over the weekend, which Sir Sadiq condemned as "utterly unacceptable".
The London mayor said "the culprits will face the full force of the law" and police were working with social media companies to try to clamp down on "viral online content which promotes violence and theft".
'Part of the broader picture'
Speaking to Sky News, M&S head of external affairs Adam Hawksbee said the Metropolitan Police's response to the chaos was "excellent".
But he said the incident in Clapham is "just part of the broader picture", with 1,600 retail workers a day experiencing violence and abuse.
"Some incidents will be serious and organised crime, and others will be individuals that are under the influence of alcohol and drugs. And this can be really scary, both for our colleagues working in the store and for the security guards," he said.
"We've had ammonia thrown in the face of one of our security guards. In the last week, we've had a store manager headbutted and these incidents are not isolated to us at M&S. They're true across the retail sector and that's why we feel like we needed to speak out."
Meanwhile, police in Rochdale issued a 48-hour dispersal order following anti-social behaviour.
Two cars were involved in a collision in the Hockley area of the city at around 11pm on Thursday, police said.
The girl was a passenger in one of the vehicles and was taken to hospital with serious injuries, but died a short while later.
Two men, aged 22 and 23, who were driving a BMW, were arrested on suspicion of causing death by dangerous driving and driving while unfit through drugs.
A woman and two other children from the same car as the nine-year-old girl were taken to hospital to be assessed by doctors, West Midlands Police said.
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The force said in a statement following the girl's death: "Our thoughts are with her loved ones at this devastating time."
A spokesperson added: "A woman and two other children from the same car were also taken to hospital to be assessed for injuries.
"Two men aged 22 and 23 from the second car, a BMW, have been arrested on suspicion of causing death by dangerous driving and driving whilst unfit through drugs."
A worker in the local area who saw the aftermath of the crash said one vehicle came to rest on a pavement near the wall of a railway bridge, with another badly damaged car left in the middle of Icknield Street, a busy dual carriageway.
A nearby resident, who did not see the crash and did not wish to be named, said: "It's a terrible tragedy for the girl's family.
"There have been fatal accidents on this road in the past, but not in the past few years. It's just a shock. It's awful."
Chloe, from Gomersal, Leeds, died in hospital after being found in the street with stab wounds in the Austhorpe area of the city just before 6am on Saturday.
Police were called on 28 March to an address in Kennerleigh Avenue, following reports a young woman had been found unconscious.
On Thursday, West Yorkshire Police confirmed another teenager had been arrested over the death and that the 14-year-old is being held in custody.
Three other teenagers have already been charged over Chloe's death, including Kayla Smith, 18, Archie Rycroft, 19, and a 17-year-old boy, who cannot be named because of his age.
All three appeared at Leeds Crown Court on Thursday for a brief hearing accused of Chloe's murder.
Smith and Rycroft, both from Leeds, appeared via videolink from separate prisons. The 17-year-old appeared via videolink from a secure accommodation unit.
All three spoke only to confirm their names and dates of birth during the 12-minute hearing.
No applications for bail were made and no pleas were made by the defendants.
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A provisional date for a trial, estimated to last more than two weeks, was set for 10 November, though the Recorder of Leeds, Judge Guy Kearl KC, said the date is subject to change and all three were remanded into custody.
The girl's father and other family members issued a tribute, saying they were "utterly devastated" and that she would "never be forgotten".
The said in a statement: "We miss every single thing about her. She was beautiful, full of joy, and had a wonderfully cheeky personality.
"She embraced life with such happiness, and she had her whole future ahead of her. Chloe was loved by everyone who knew her, and the absence she leaves behind is immeasurable."
Chloe's mother said in a separate tribute she "cannot put into words" the loss of her "beautiful princess".
She added: "You are my life, my world, my best friend and I know that I am yours. I cannot live without you - I need you."
Min Aung Hlaing, 69, who is a senior general, won 429 out of the 584 votes in Friday's ballot, Aung Lin Dwe, speaker of both the upper and lower house, said.
The run-off, which was broadcast live, was held in the newly renovated parliament building in the capital, Naypyidaw, which was damaged in last year's earthquake.
His victory was expected as the chamber is dominated by the pro-military Union Solidarity and Development Party (USDP) and members appointed by the armed forces.
It follows a landslide victory for the army-backed USDP in a general election held in December and January.
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Critics and Western governments dismissed those polls as a sham to continue military rule behind a facade of democracy.
Min Aung Hlaing has led the nation since orchestrating a coup against the government of Aung San Suu Kyi in 2021, leading to a civil war.
The Nobel Peace Prize winner was arrested, sparking widespread protests that turned into nationwide armed resistance against the junta.
Ms Suu Kyi, 80, is serving a 27-year prison term on charges widely viewed as politically motivated.
The general, who has led the armed forces since 2011, has long coveted the presidency, according to independent Myanmar analyst Aung Kyaw Soe, who said "it appears his dreams are now becoming a reality".
On Monday, Min Aung Hlaing stood down as commander-in-chief because the country's constitution prohibits the president from simultaneously holding the top military position.
As he was nominated in parliament as a presidential candidate, he proposed Ye Win Oo, a former intelligence chief seen as a fierce loyalist, as his successor to lead the military.
Earlier this week, some anti-junta groups - including those containing remnants of Ms Suu Kyi's party and longstanding ethnic minority armies - joined forces in a new combined front to take on the military.
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The Steering Council for the Emergence of a Federal Democratic Union said on Monday that they wanted to "completely dismantle all forms of dictatorship" and "collectively initiate a new political landscape".
Resistance groups could face intensified military pressure as well as increased scrutiny from neighbouring countries that may seek to bolster their relationship with Min Aung Hlaing's new administration, analysts said.
The military handover and Min Aung Hlaing's rise to the presidency are seen by analysts as a strategic pivot to consolidate his power as head of a nominally civilian government and earn international legitimacy, while protecting the interests of an armed forces that has run the country directly for five of the past six decades.