A man has been arrested on suspicion of causing death by dangerous driving after a schoolboy was killed.
Emergency services were called to Stock, near Billericay, Essex, at about 08:20 GMT, to reports of a vehicle hitting two children.
A boy died at the scene and the second child was taken to hospital. Both were pupils at the village high school.
The 23-year-old man is also being questioned on suspicion of driving whilst unfit through drink or drugs.
He was further arrested on suspicion of causing serious injury by dangerous driving, and remains in custody.
Det Insp Mark Fraser said: "This is quite clearly an incredibly tragic incident which will be felt by many people across the area, not least the families of the two young victims.
"Our role is to establish the circumstances which led up to this incident, which we will do meticulously and I would ask people not to speculate, whether in person or online."
Mayflower High School in nearby Billericay, where both children were pupils, said it was "shocked and immensely saddened".
"We are supporting all of our children and staff today as we try to come to terms with this sad loss," said headteacher Damian Lee.
"We are a strong and close community and will ensure that everybody is given the necessary help."
Stock Road was closed between School Lane and Honeypot Lane and Essex Police said they expected closures to remain in place for some time.
Officers urged people with dashcam footage or additional information to come forward.