'Pushy parents' who demand results from doctors can unwittingly be harming their child's health, researchers warn.
There is no physical cause for the stomach pains
A study by Institute of Child Health experts looked at cases where children suffered unexplained abdominal pain.
Despite doctors carrying out the necessary tests and finding no physical cause, parents refused to accept the medical team's conclusions.
The Archives of Disease in Childhood study warned that this can extend the child's suffering.
Functional abdominal pain causes severe stomach ache, and often vomiting, and affects up to one in 10 children.
It can lead to children being admitted to hospital but there is no known physical cause, although stress and other psychological factors can make symptoms worse.
Parents are often unwilling to accept that there is no cause and assume doctors have missed something, subjecting their children to tests they do not need and taking them to other specialists to try to determine a cause for their child's illness.
In this study, doctors looked back at 23 cases of children with unexplained severe abdominal pain referred to Great Ormond Street Hospital between 1997 and 2001.
They had all undergone checks, including blood tests, ultrasound and endoscopy.
Fifteen had already been seen by at least two consultants before they were seen at Great Ormond Street.
Two of the children had seen seven doctors prior to their referral.
Seven families had asked for extra tests to be carried out, even though there was no clinical indication they were necessary. Only two were successful, and in neither case did the results change the diagnosis.
Many parents had lost faith in the medical profession and were aggressive or confrontational with the GOSH doctor.
Twelve families made a formal complaint about the care their child received, hoping to persuade doctors into carrying out more investigations.
And, despite the link with psychological factors, only 13 families accepted referral to psychological services.
In 12, a high degree of family conflict or dysfunction had been seen, and parents were unaware of the potential impact this could have on their child's illness.
Eleven of these children improved after psychological support and resumed normal activities within a year.
Of the 10 families who refused psychological help, only three children eventually improved.
In each of these cases, the families accepted the role psychological factors played.
Writing in the Archives of Disease in Childhood, the researchers, led by Dr Keith Lindley, said: "The study of children with FAP illustrates the dangers of 'healthcare consumerism' in families who lack insight into the origins of their child's symptoms and how this can lead to an abuse of the hospital's complaints procedures which risks compromising the child's physical wellbeing."
They added: "Robust systems are needed to protect the child, and perhaps their physician, from the effects of healthcare consumerism."
Dr Harvey Markovitch, spokesman for the Royal College of Paediatrics and Child Health, told the BBC News website: "I think all paediatricians reading this paper will find its conclusions very familiar.
"What it showed was those who know their rights and wanted them, in the main, didn't seem to help their child at all.
"All they managed to do was upset their doctors and cause their children to be over-investigated."