A six-year-old boy died after being hit by a car in Thamesmead hours after a 10-year-old girl was knocked over by a van less than a mile away.
Witnesses spoke of the horrific moments following the fatal accident at the junction of Kale Road and St John Fisher Road just outside Harlequin House on Thursday at 6.15pm.
Police say the boy was walking along the road with his mum and family members.
He is believed to have stepped out from behind a white van when he was reportedly hit by a Honda CRV.
Darren Carr, of Dexter House, was one of the first people on the scene with his partner Nicole and they ran out of their home when they heard a "thud".
The 42-year-old said: "I heard a loud bang and we came down to see what was happening.
"The family were covered in blood and we tried to help clean them up. They were all screaming.
"The mum scooped up the boy up off the floor and they got in a passing car to take him to hospital.
"I just thought it was game over.
"His shoes and rucksack were left strewn in the road and I just put them to one side."
The driver who hit the child was described as a "well dressed man in his twenties" who stopped at the scene and was not arrested.
A witness who lives in Harlequin House said she heard a "loud bang" and could see he accident from her balcony.
She added: "I was ringing the ambulance and screaming at the mum to not pick him up and leave him on the floor.
"It's a mother's instinct to pick up her baby though.
"There was so many people out and police everywhere.
"I have not been able to sleep, it was the worst thing I have ever seen."
A card saying "RIP angel" was left at the scene along with flowers and a teddy bear.
Mother-of-two Kelly Heavens, 38, of Kale Road, Thamesmead, called for more speed restrictions around the area.
She said: "We need safety improvements round here, it has taken for a child to die. It is ridiculous, you can't see where the road ends and the pavement begins."
A Met Police spokesman said: "The driver of the car stopped at the scene and no arrests have been made."
Anyone who witnessed the collision is asked to call the Serious Collision Investigation Unit on 020 8285 1574.
Hours earlier, a 10-year-old girl was taken by ambulance to King's College Hospital with serious injuries, believed to be a broken leg, after an accident just before 1pm.