A two-year-old with a twisted bowel died despite her mother telling NHS non-emergency services about "blue lips and breathlessness", a coroner said.
Myla Deviren's mother spoke to a series of NHS 111 and out-of-hours service advisors, but none "appreciated" her symptoms and she later died.
A coroner said with earlier hospital transfer and appropriate treatment Myla probably would have survived.
The 111 provider said it had made a number of changes since Myla's death.
In a prevention of future deaths report Rosamund Rhodes-Kemp, assistant coroner for Cambridgeshire, said after Myla, of Peterborough, became unwell in the early hours of 27 August 2015 her mother rang 111.
During the call the health assistant "did not appreciate the significance of key symptoms", Ms Rhodes-Kemp said.
Myla's mother was passed to a clinical adviser, whom Ms Rhodes-Kemp said "ignored her instincts" to call an ambulance after hearing the little girl had blue lips and breathlessness.
The call was then passed to an out-of-hours nurse who "decided that this was a case of gastroenteritis early in the call and did not appreciate the description of a child with worsening signs".
Myla was later found unresponsive and despite being taken to hospital by ambulance was pronounced dead later that day.
The coroner said: "It is probable that with earlier transfer to hospital by ambulance and with appropriate treatment [Myla] would have survived."
Ms Rhodes-Kemp said that further steps in the 111 and out-of-hours services should be taken, including mandatory annual training for all call staff and having a "suitably-qualified" paediatric specialist clinician available.
She added the "default position and precautionary advice should be - if in doubt call an ambulance".
The chief executive of Cambridgeshire Community Services (CCS), which ran the out-of-hours service at the time of Myla's death, "reiterated our sincere apologies" to her family following the inquest earlier this year and said it made "improvements" before transferring the service in 2016.
A spokeswoman for Herts Urgent Care (HUC), which runs 111 services and took over out-of-hours from CCS, said it had "made a number of changes to its service since Myla's death which relate to concerns raised by the coroner".
Carol Anderson, chief nurse at Cambridgeshire and Peterborough Clinical Commissioning Group, said it worked with NHS 111 providers "to ensure all recommendations and learnings from the coroner's report have been implemented and are monitored on an ongoing basis".