GPs are failing to carry out basic checks on children with fever that could flag up life-threatening illnesses, research suggests.
A new study found most under-fives with a high temperature are not checked properly for signs that could indicate sepsis, meningitis or pneumonia.
The National Institute for Health and Care Excellence (Nice) published guidelines in 2007 and again in 2013 urging GPs to carry out four simple tests.
But evidence suggests they are still not being done and charities said lives are being needlessly lost as a result.
The Nice guidance says GPs must measure and record temperature, heart rate, respiratory rate and capillary refill time "as part of the routine assessment of a child with fever".
Capillary refill is when doctors press on a patient's nail bed and then count the seconds until it returns to its usual colour - normally under two seconds.
In the new study, Dr Alice Lee, from Pennine Acute Hospitals NHS Trust, looked at data for 47 children under five in a Stockport GP practice.
She found that just 13% of consultations included all four checks, with around one in three children receiving no tests at all or only one.
Despite the fact abnormal respiratory rate "is often the first sign of serious illness", Dr Lee said it was the lowest-recorded test, with only 30% of children being checked.
Almost half of youngsters also missed out on having their pulse taken, while a quarter did not have their temperature recorded.
However, when GPs were given crib sheets as reminders, there was a marked improvement in performance, with the number of children receiving all four tests almost doubling.
Dr Lee said most children with a high temperature have a self-limiting viral illness, which will fully resolve without any harm to the child.
"However, differentiating these children from the ones who then go on to develop the serious infections, the serious illnesses, can be incredibly tricky," she said.
"Despite everything that we are doing, sepsis still continues to be an issue, and infection is the leading cause of death for children under the age of five.
"There has been a really big push recently to recognise sepsis and serious infection as a medical emergency."
Dr Ron Daniels, chief executive of the Sepsis Trust, said the failure of doctors to carry out all four checks had been implicated in several deaths, including those of three-year-old Sam Morrish from Devon and 12-month-old William Mead from Cornwall.
He said: "We are aware this is a problem and we are seeing this not only with children but with adults too.
"Basic observations are not being done routinely and, where observations are being done, they are not being done as a complete set.
"In the majority of cases, GPs will be able to make the right decision but it's clear we are still missing some cases."
A Health Service Ombudsman's report into the death of Sam Morrish was highly critical of the way GPs had failed to follow the Nice guidance and had not checked his breathing or heart rate.
Melissa Mead, William's mother, said: "Two of the four basic observations were not carried out during the last consultation with the doctor before William died.
"Had these been done, the pneumonia and sepsis that William was suffering with would have been detected and he would have received life-saving treatment. I am disappointed to hear that the basics are still being ignored.
"Until those in frontline primary care observe the basics, life-threatening conditions will be missed and people will continue to die in preventable circumstances."
Scott Morrish, Sam's father, said: "Six years on from Sam's death, it's disappointing that these basic checks are being ignored."
He added that there was a need to raise awareness among parents of the four checks alongside symptoms to look out for.
Parliamentary and Health Service Ombudsman Julie Mellor said: "Too many people are still dying unnecessarily from sepsis."
She said that since her 2013 report into sepsis, the Government and NHS have taken steps to improve diagnosis and treatment, including new guidance from Nice and a commitment to improving awareness of the condition.
"This will be vital in order to save lives," she said.