An expert claims controversial changes to GPs' contracts may mean serious illnesses in children are being missed.
Dr Anthony Harnden, a lecturer in general practice at Oxford University, is concerned over the different experience and skill levels of staff overseeing care after GP surgeries close.
And he added there should be less advice given out over the telephone, and more face-to-face assessments.
The government negotiated a contract with GPs in 2004 which led to more than 90% opting out of providing out-of-hours care, with responsibility moving to primary care trusts.
But Dr Harnden, writing in the British Medical Journal (BMJ), said: "Changes in NHS policy have led to the primary care of febrile (feverish) children presenting outside office hours being delivered by an increasing number of professional groups.
"Doctors, nurses, staff working for the telephone helpline NHS Direct, out-of-hours centres and accident and emergency departments may all have different levels of skill and experience.
"This is a major concern because the most solid evidence for recognising clinical severity in febrile children in primary care is a global assessment by an experienced clinician.
"The global assessment involves eliciting a clear history and careful observation of signs, including alertness, activity, colour and respiratory effort."