At 09.05hrs on Saturday, 3 August, police were called to a bus in collision with two children on Watling Street near the junction with Halcot Avenue, Bexleyheath.
A nine year-old girl was taken to hospital by ambulance. Her injuries are being treated as life-threatening.
A five year-old boy was taken to hospital as a precaution.
The children are siblings who were with a family member at the time of the collision. Officers are providing support to their family.
The male driver of the bus was arrested. He has been taken into police custody where he remains.
Any witnesses to the collision who are yet to speak with police are asked to call 101 quoting reference 2309/03Aug.
