The poignancy of this question coming from someone so young -- with many families feared among the victims
-- was lost on no one. The mayor told the boy: "I know you're angry and we're going to get answers," but this reassurance did not stop other residents, angry over the disaster itself and problems over coordination of the relief effort, heckling as the mayor tried to speak.
Despite the angry confrontation, at least Khan met residents face to face -- unlike British Prime Minister Theresa May, who was criticized for making a private visit to the scene Thursday, meeting only police officers and firefighters. On Friday, May's office announced she would be visiting victims in a nearby hospital.
The mayor's response -- to keep talking to Londoners even in the face of anger -- is in keeping with a man who has shared in the city's many traumas over the past few months.
Within hours of the devastating tower fire in west London
on Wednesday, Khan was due to attend a ceremony to mark the reopening of Borough Market, the site of the terrorist attack
just 11 days earlier. The event was intended to be one of unity and defiance against the attackers who murdered eight people in the food market and on nearby London Bridge.
Instead the occasion took on a renewed sense of sadness as the blaze at the tower block still raged a few miles away.
These two disasters, together with the Westminster Bridge attack
back in March, have given the capital more than its fair share of trauma in the past few months. For Khan, they have contributed towards a testing first year in office.
The mayor had been woken up by senior City Hall and fire officials in the early hours of the morning to be told that an uncontrollable fire was ripping through the 24-story Grenfell Tower in North Kensington.
He tweeted shortly afterwards that a "major incident" had been declared. He was briefed by the city's "gold command" -- the highest level of police and emergency service officials.
Despite the unfolding tragedy, Khan was determined to go ahead with the poignant visit to Borough Market, where he had to deliver a statement detailing how yet another tragedy had befallen the city.
His response was more personal than political: he spoke of how he was "truly devastated to see the horrific scenes of the major fire at Grenfell Tower in Kensington."
Visiting the scene of the fire after the Borough Market ceremony, there was anger in Khan's comments too, saying he would demand questions were answered at how the tragedy could have happened.
His emotional response underscores how Khan is seen as a Londoner first, politician second.
Khan was born and raised in London, growing up in Tooting, in the south of the city, to bus driver and seamstress parents who had emigrated from Pakistan. His first home, where he lived with his parents and seven siblings, was a modest three-bedroom council flat in a community not dissimilar to the neighborhood where the fire struck.
His mayoral campaign of 2016 -- which followed 11 years as an MP including several as a minister in the last Labour government -- was built on addressing inequality and uniting different communities in the city. Khan, London's first ethnic minority mayor, has a down-to-earth style -- which helped him win the most votes
any individual politician in the UK has ever received.
His low-key style contrasts sharply with his predecessor, now Foreign Secretary Boris Johnson, whose flamboyance and humor
always prompted doubts over whether he was a serious enough politician to oversee a city in tough times. It turns out he didn't need to. While Johnson had the 2012 Olympics and Queen's Diamond Jubilee in his city, Khan's first year has been overshadowed by more tragedy than in Johnson's eight years in office.
A month after Khan's election, the UK voted for Brexit
and during his first year there have been fears over how London will change once the country leaves the EU -- particularly its financial sector, heavily dependent on trade with Europe.
As a Londoner and as the city's first Muslim mayor, Khan has been able to provide a unifying voice in the aftermath of each of these tragedies. Addressing a vigil held after the London Bridge attack, the mayor gave a powerful speech denouncing the attackers, saying: "As a proud and patriotic British Muslim I say this, you do not commit these disgusting acts in my name.
"Your perverse ideology has nothing to do with the true values of Islam. You will never succeed in dividing our city."
And after the Grenfell Tower fire, Khan will be able to provide an important link between a community angry at being neglected and those in positions of power.
After the London Bridge attack earlier this month, Khan tried to reassure Londoners that, despite some media reports, the city was not reeling or under siege, and said there was "no reason to be alarmed" by increased police presence.
This comment drew an extraordinarily sharp rebuke from US President Donald Trump on Twitter. When the mayor responded by saying his remarks had been taken out of context because he had been referring to the enhanced police presence, Trump tweeted: "Pathetic excuse by London Mayor Sadiq Khan who had to think fast on his 'no reason to be alarmed' statement. MSM is working hard to sell it!"
Their feud escalated
when Khan said the UK should not "roll out the red carpet" for President Trump, which may have contributed to the White House reportedly delaying a forthcoming state visit (a report the administration has denied).
The dispute also showed how strongly Khan feels about his city as it endures difficult times.