Two children were rushed to hospital this morning after being hit by a van at a pedestrian crossing.
One of the four youths suffered serious head injuries following the crash, which happened at around 8am in Basildon, Essex.
The second child, only two years old, was also injured in the collision.
The driver of the van stopped at the scene and Essex Police are appealing for witnesses to come forward.
Police said: 'We are appealing for witnesses to a collision in Basildon in which two young children have been injured, one seriously.
Officers received reports that a van had collided with two young children at a junction in Broadmayne at around 8am this morning.
'A four-year-old child suffered serious head injuries and was taken to hospital for treatment.
A two-year-old child was also injured, but less seriously.
The vehicle, a white Citroën van, stopped at the scene and our investigation is ongoing.
'If you have any information, CCTV, dashcam or other footage relating to this incident please contact us.
'Quote 238 from August 16.
You can let us know by making a report on our website or by using our online Live Chat service, which is available 24 hours a day, 7 days a week.
Please visit our website for more information about our online reporting services.
'If you would like to make a report anonymously, you can contact the independent Crimestoppers foundation. You can do this by visiting their website or by calling 0800 555 111.'