A two-year-old boy and his mother were shot in a "wanton act of indiscriminate violence", police have said, after a gunman opened fire then fled on a motorbike.
The child and his mother, aged in her twenties, along with two men in their late teens, were taken to hospital after the shooting in north west London on Wednesday night.
Multiple shots were fired at the group in Energen Close, Harlesden, before the gunman jumped on a motorbike and fled.
The child is in a serious but stable condition in hospital, while the other three adults have suffered non life-changing injuries.
Detective Chief Inspector Rick Sewart, of the Metropolitan Police, said the "terrible crime" had left the "innocent" boy seriously ill and pleaded with anyone with information to come forward.
"This child was shot in a wanton act of indiscriminate violence," he said.
"I know that people will be shocked and horrified that a little boy should be the victim of a gunman and I need the community to show their support for him, and his family, by telling police what they know.
"Anyone giving information will be fully supported and if you don't want to give your name, you can call Crimestoppers, which is totally anonymous.
"But however you want to do it, make that call, and anyone who is doubtful should think of that little boy and his family's anguish."
Police were called to the scene at 9.45pm to reports of "shots fired". No arrests have been made.
A neighbour, who was at home alone with her young son, said she heard screaming and saw crowds gathering in the area.
"My neighbour went out to help one of the men who was shot," the 34-year-old said.
"She told me that the bullet had gone through his shoulder and she was pressing the wound to stop the blood flowing."
One neighbour, 63, said the incident was "very disturbing and quite unsettling".
Another eyewitness said she saw the boy being taken into an ambulance with a gunshot wound to his neck.
North West Borough Commander, Roy Smith, added: "This violent incident in itself is shocking but even more abhorrent is the fact that one of the victims is a young child.
"As a child is battling for their life, I urge everyone in the local community to support us by coming forward with any information that will help us make arrests."