The car they were travelling in on Valentine’s Day with the boy’s 20-year-old aunt was ambushed on Chicago’s West Side by another man.
The toddler, named as Lavontay White, was sitting in the back seat of the red sedan and was shot in the head.
He died in hospital, becoming the third child to be shot dead in the city in four days.
His aunt and uncle were in the front, filming the journey.
Footage shows the pair singing along to rap music when they are shot at.
A number of shots can be heard in quick succession as the woman, who has not been named, screams and runs out of the car.
She was reportedly pregnant. Despite suffering a wound to her stomach, she and her unborn child survived.
Police hunting the suspect are examining the footage and said the man who died, identified as Lazarec Collins by officials, was the intended target of the gang-related attack.
Images showed officers at the scene and examining the vehicle which had several bullet holes in it.
Police chief Eddie Johnson said: “This has just got to stop somewhere.
“Our children shouldn’t have to keep paying the price for our inability to hold repeat gun offenders accountable for their actions.
“I’m sick of it, and I know Chicago is sick of it.”
If Chicago doesn’t fix the horrible “carnage” going on, 228 shootings in 2017 with 42 killings (up 24% from 2016), I will send in the Feds!
— Donald J. Trump (@realDonaldTrump) January 25, 2017
On Saturday, 11-year-old Takiya Holmes was shot in the head while travelling on the back seat of a van on the city’s South Side. She died three days later.
Antwan Jones, 19, has been charged with murder after he turned himself in to police.
Twelve-year-old Kanari Gentry-Bowers was shot while playing with friends outside a school on Saturday. She died four days later.
Donald Trump has repeatedly voiced his concern about the growing violence in Chicago. He threatened to “send in the Feds” to fix the problem in a tweet on 24 January.
So far this year, there have been 63 murders – more than double the number for the same period two years ago.
Last year, there were more than 750 murders and 3,500 shootings.
Mayor Rahm Emanuel said in response to the shootings: “When innocent children are caught in the crossfire of gun violence and young people have their childhood stolen by stray bullets, our consciences are shaken, and our hearts are broken.”