A boy has been hospitalised with potentially life-changing head injuries after he was attacked in a Milton Keynes park.
Three teenagers received injuries after being chased by two men - one who was hospitalised sustained a fractured skull which required surgery.
Two others sustained lumps and grazes to their head and or hands.
Thames Valley Police is appealing for information following the incident which took place between 7.30pm and 8pm on December 14.
The boys were sitting in the two swings park area between Gibbwin and Malins Gate, Great Linford, when they were approached by two men, one of whom was carrying a baseball bat.
The first offender is black, around 5ft 9in-5ft 10ins, of medium build - he was wearing a black hooded-top with the hood up, black tracksuit bottoms with a big black parker-style jacket with fur around the hood. He was carrying a baseball bat.
The second offender is black, around 5ft 11ins, skinny, and was wearing a black balaclava, a black hooded-top with the hood up and black jeans.
Investigating officer detective constable Serena Bellis, said: “This was a vicious attack in which one of the victims has suffered potentially life-changing injuries, while two others suffered minor injuries.
“Anyone with information can contact Thames Valley Police via the non-emergency number 101.
“If you don’t want to speak directly to police you can contact the independent charity Crimestoppers anonymously on 0800 555 111.
“No personal details are taken, information is not traced or recorded and you will not go to court.”