A hospital trust has taken full responsibility for 24 failures that led to the death of a 21-month-old.
Eleanor Hazel Aldred-Owen died at Liverpool's Alder Hey Hospital on 2 October 2023 - a coroner concluded she died as a result of misadventure, contributed to by neglect.
She had routine surgery for craniosynostosis, external, a birth defect affecting the skull, but an abnormal chest X-ray was not flagged.
Eleanor suffered a cardiac arrest and unsurvivable brain injury and died in her parents' arms.
Her family, from Mold, Flintshire, said they had lived with "unbearable" guilt and trauma ever since.
Alder Hey Children's Hospital NHS Foundation Trust said her "tragic" death "should not have happened".
Eleanor's dad Chaz said: "Not knowing how or why Eleanor died was the key factors and what kept us going was justice for her.
"The real victory is making sure what happened to Eleanor doesn't happen to anyone else. No other family or child will have to go through what we have."
He added both he and his wife Rachel were "fairly certain it was neglectful" but did not realise the extent of it, and were "at the mercy of what Alder Hey were telling us".
"They said it was breach of duty and not gross neglect and it took a long time for the trust to admit that."
He said the trust "being compelled to admit gross neglect" was the hardest thing.
Eleanor had routine surgery for craniosynostosis on 29 September 2023 and it went as planned, apart from the accidental removal of the breathing tube used during anaesthetic which was replaced by the anaesthetist and the procedure continued.
During recovery, Eleanor had a raised heart rate and needed oxygen, and a decision was made to start AIRVO, a type of high-flow humidified oxygen, which was undocumented and not prescribed in accordance with the trust's guidelines.
After her operation, Eleanor developed a collapsed lung as a result of surgery.
A radiographer failed to flag her abnormal chest X-ray to anyone on the ward, and the doctor did not review it immediately because she was in A&E reviewing another child.
Eleanor had a cardiac arrest before the collapsed lung was identified and treated, causing an unsurvivable brain injury.
An investigation found there were 24 failures in care that resulted in her death.
These included failure to correctly calculate her Paediatric Early Warning System, external score on several occasions, which would have led to a much earlier medical review and chest X-ray.
In a statement, her family said: "Eleanor's death was preventable and should not have happened.
"As parents, the guilt is unbearable, even though we know Eleanor was failed by the trust and not by us. We are irreversibly changed as people.
"We don't just constantly grieve for her, we grieve for the people we used to be when our daughter was here."
They said they recognised the changes the trust has implemented following Eleanor's death, but that these had to be "used properly, kept under review and make care safer for other children".
Chaz said two post-operative procedures had been brought in to Alder Hey and named after Eleanor, and the changes the hospital had put in place was Eleanor's legacy and something he and his wife could be proud of.
Lynda Reynolds, the family's solicitor and partner at Hugh James, said it was "an unimaginably tragic case".
"Eleanor's parents placed their trust in Alder Hey Children's Hospital to care for their daughter and were let down," she said.
"For Eleanor's family, the trust's acceptance of responsibility and public apology are important, but this follows a long and painful process.
"We hope that the changes the trust have implemented continue to make care safer for other children."
