The crash happened as the boys were going to a birthday night out

The accident happened on the A4142 on Saturday when a Citroen Xsara, driven by a 45-year-old woman and carrying the seven boys, hit a Honda Civic.

All the boys involved in the crash were aged 12 or 13 and were going out to celebrate a friend's birthday. The woman driver was also critically hurt.

Honda driver, Howard Hillsdon, 21, of Yarnton, also died in the crash.

His family released a statement which said that he was "an outgoing young man" who "will be desperately missed".

No-one else involved has yet been formally identified by police.

We are keeping an open mind about possible causes and will be using all the skills we have to piece together how the collision occurred Supt Mick Doyle

Officers said the boys were on an evening out to celebrate the 13th birthday of the 45-year-old Citroen driver's son when the five-seater vehicle went into the opposite carriageway, hitting the Honda.

The boy is believed to have survived the crash, while his mother is too ill to talk to police about what happened.

She was airlifted to the Great Western Hospital in Swindon where she is said to be in intensive care with severe neck injuries.

Two of the boys, both aged 13, died at the scene, while a third 13-year-old and Mr Hillsdon died later at the John Radcliffe II hospital in Oxford.

The four injured boys were also taken to the hospital.

The A4142 is a major bypass around the city

A passenger in the Honda was flown to the Stoke Mandeville Hospital in Aylesbury but police say his injuries are not serious.

The drivers of a Volkswagen and an Audi that both drove into the back of the Honda were treated for minor injuries.

A motorcyclist who crashed nearby after braking hard to avoid the pile-up also needed medical treatment.

Supt Mick Doyle, head of Thames Valley Police's roads policing unit said: "This incident has been challenging and distressing for all involved and my officers continue to work to establish what happened last night to cause this tragedy.

"We are keeping an open mind about possible causes and will be using all the skills we have to piece together how the collision occurred.

"This remains our focus in the coming days and we are also working to support the family and friends of those involved. They have our deepest sympathies and we will offer them all the help we can."