Police have named five people who died in a head-on collision in Derbyshire.
Kenneth and Martin Jones were among the five people killed
Brothers Joshua and Leon Taylor, seven and four, died when their mother's Renault was in collision with a Ford Sierra near their Shuttlewood home.
Three men in the Sierra died. They were brothers Kenneth and Martin Jones, 25 and 22, and Andrew Darnell, 21, all from Bolsover.
The police are investigating whether the Sierra was racing a motorbike when the accident happened on Saturday.
A 17-year-old motorcyclist has been arrested.
Joshua and Leon Taylor's mother was seriously injured and is in hospital along with her 13-year-old nephew.
All of the victims were pronounced dead at the scene on Chesterfield Road, where flowers and messages have now been left.
Supt Kevin Lea said: "The officers who are dealing with it are saying that it's one of the worst they have dealt with, not only because children are involved but because of the extent of the damage caused and the number of casualties.
"One line of inquiry is that there may have been some form of racing between a trials-type motorbike and the Sierra as it went down towards where the crash happened."
He said officers wanted to hear from anyone who witnessed the collision or saw either of the cars in the area, or a trials-type motorcycle.
The incident happened about 1515 BST on Saturday.