Police have said the child is in a serious condition and are waiting for updates on the health of three adults also injured in the incident in Hackney.
All four were taken to hospital with gunshot injuries, Sky News reported.
Officers were called to the scene in Kingsland High Street at about 9.20pm on Wednesday, according to the Metropolitan Police, with specialist firearms officers attending.
No arrests have been made and police are still investigating the circumstances of the shooting.
Deputy assistant commissioner Matt Ward said: "We know Londoners will be shocked by what has taken place tonight.
"Our thoughts go to all those affected.
"Fast-moving inquiries are underway and we will update as soon as we can. If anyone has any information, please contact us."
A London Ambulance Service spokesperson said: "We sent resources to the scene, including ambulance crews, advanced paramedics, incident response officers and members of our tactical response unit.
"We also dispatched a trauma team from London Air Ambulance, which consisted of a doctor and a paramedic in a car.
"We treated three adults and one child at the scene before taking them all to a major trauma center."