Four teenagers have been arrested on suspicion of murder after a 12-year-old girl suffered “catastrophic injuries” after being assaulted in Liverpool, police have said. Ava White had been out in the city centre with friends when she was attacked at 8.39pm on Thursday, shortly after the Christmas lights switch on took place. A member of the public who witnessed the child collapsing administered first aid before she was rushed to Alder Hey Children’s Hospital, where she died. Officers arrested four schoolboys – one aged 13, two aged 14 and a 15-year-old – in the Toxteth inner-city area of the city on suspicion of murder. Merseyside Police assistant chief constable Jon Roy said officers believe the victim and her friends had been involved in an argument before she was attacked. The force previously said Ava had been stabbed but later said a post-mortem examination would be carried out to establish the cause of death. “Our thoughts and condolences go out to Ava’s family, who are being supported by specialist family liaison officers,” Mr Roy said. “Their world has been torn apart and no parent should ever have to face that knock on the door from police officers to say that their child has died. “We believe that Ava and her friends had been involved in a verbal argument which culminated in Ava being assaulted, causing catastrophic injuries. And we understand that the offenders were then seen to run up School Lane across Hanover Street and on to Fleet Street.” He said the area was “very busy” when the young girl was assaulted and urged witnesses and people who may have mobile phone footage or photos of the incident to come forward to help police with the investigation.