When three-year-old Jonnie Meek died at the scandal-hit Stafford Hospital last year, an inquest initially decided natural causes were to blame.
But on Friday, a new inquest was ordered after his parents discovered key witnesses had not been called and medical notes contained incidents that never happened.
Video report by ITV News correspondent Richard Pallot
Jonnie was only in hospital for a routine procedure. Two hours later, he was dead.
"The new inquest, with the proper witnesses that should be available and all the evidence that has now been seen, it should come to the correct conclusion which is...that it was an allergic reaction to this milk," his father John Meek told ITV News.
April Keeling, his mother, added: "We just want to prevent it from happening to anybody else and we just want to let Jonnie rest."
North Midlands NHS Trust said they welcome the review.