The UK and US have agreed to end the "anomaly" that allowed the woman suspected of causing Harry Dunn's death to claim diplomatic immunity.
A court heard last month that the "secret agreement" permitted Anne Sacoolas to return to her home country after a road crash which killed the 19-year-old in August last year outside RAF Croughton in Northamptonshire.
Despite the document now being amended, Harry's alleged killer still remains in the US.
His mother Charlotte Charles said the announcement was a "huge step forward" - adding that one of the family's aims was for this to "never happen to another family again".
But she added their campaign would continue for Ms Sacoolas to be brought back to the UK.
Foreign Secretary Dominic Raab said the changes mean a similar tragedy "could not happen again".
He added: "I know these changes won't bring Harry back, and I appreciate the pain and suffering the family are still going through.
https://news.sky.com/story/harry-dun...omaly-12033855