Officers were called at approximately 8.15pm on Friday, 9 July, to reports of a road traffic collision in Sipson Lane, near to the High Street.
It was reported a moped, travelling towards the High Street, had been involved in a collision with a six-year-old boy and failed to stop at the scene.
The child was treated at the scene before being taken to hospital, where he is in a critical but stable condition.
An image of a moped with two people police would like to identify has been released by police.
No arrests have been made at this time.
Officers from the Serious Collision Investigation Unit (SCIU) are investigating. They are particularly keen to hear from any drivers who were in Sipson Lane from 20:00hrs onwards and who may have recorded the events leading up to the collision on dashcam.
Any witnesses yet to speak with police are asked to call the SCIU at Alperton Traffic Garage on 020 8246 9820 quoting CAD 7022/09July.