A panel of experts reviewed 126 deaths in one year and found 'avoidable factors', such as doctors misdiagnosing a serious illness or giving the wrong treatment, in 26 per cent of cases.
A further 43 per cent were due to 'potentially avoidable factors' – including missing important immunisations or delays in treatment.
Tragedy: Nine-month-old Liam Eaves died in 2004 after meningitis symptoms were misread. His parents were awarded a five figure out-of-court settlement in March
The study, by the Confidential Enquiry into Maternal and Child Health (CEMACH), found that in two thirds of the cases, the children died in hospital, many of them on emergency wards staffed by a high ratio of junior doctors with little paediatric training.
The review, the first of its kind, was funded by the Department of Health. It highlighted the fact that levels of experience and standards of care for children 'vary considerably' across the country.
It states: 'We have found, throughout this review, examples of failure to make thorough examinations and correctly interpret clinical signs. In some cases these failures have made significant contributions to the child's death.
'The errors concerned were repeated and compounded by the fact that the principal assessment was being performed by a junior doctor with no postgraduate training in paediatrics in settings where there was no supervision by an experienced specialist or paediatrician.'
The study team collected data on children under 18 who died in 2006 and the experts evaluated more than 120 deaths in detail. Around 3,000 children die in Britain every year.
Deaths were categorised as 'avoidable' if the panel found 'failures in the child's direct care by any agency with responsibility for the child'.
They were classed 'potentially avoidable' if no agency was directly involved with a child's care but should have been.
In one case highlighted by the report, a seven-month-old baby was twice sent away from a hospital's emergency ward just hours before dying from meningitis, after a junior doctor wrongly blamed the fever on a routine immunisation.
A ten-year-old boy known to have high blood pressure died of a brain swelling after nurses failed to read his blood pressure and lost his medical notes.
And one GP sent a baby with worsening breathing problems home to wait for an ambulance, during which time the child died.
The study criticised doctors for failing to examine and observe sick children properly, failing to recognise serious illnesses and their complications and not following published guidance on treating child patients.
There were also examples of cases where medical records were incomplete or inaccurate.
Conservative health spokeswoman Anne Milton said the report sent a 'sobering' message to Government.
'It is important Ministers take into account the advice to help reduce avoidable deaths,' she said.
The College of Emergency Medicine said it was 'fully aware' of inadequacies in emergency departments, which treat 3.5million children every year.
It said medical school prepared graduates very poorly for paediatric emergency care.
The Royal College of Paediatrics and Child Health also called for improved training.
Acknowledging the importance of the report's findings, Dr Sheila Shribman, National Clinical Director for Children, said: 'We will look to the National Patient Safety Agency to work with CEMACH to consider how to take this important work forward.
'The inquiry also found many examples of high-quality care – there is much good practice we can all learn from.'
