The overwhelming majority of parents whose children have cystic fibrosis want gene therapy trials to go ahead, bypassing normal research guidelines.
Cystic fibrosis causes respiratory problems
Great Ormond Street Hospital scientists hope to test gene therapy on children.
But, in a Journal of Medical Ethics paper, they suggest ethical worries about testing on children without prior tests on adults will prevent the work.
They fear studying adults, whose lungs are by that stage badly affected, would not show if children could benefit.
One in 25 people carry the faulty gene which causes the condition.
Cystic fibrosis experts said it was recognised that gene therapy trials needed to be carried out on those who might benefit.
A survey of 78 parents of children with cystic fibrosis by GOSH researchers found virtually all were in favour of gene therapy trials going ahead, and just over 90% would enrol their own child.
Just over half hoped gene therapy would lead to a cure for CF.
Aim 'to halt damage'
Cystic fibrosis is the most common single gene disorder in white Caucasians.
It is a life-limiting inherited genetic disease which affects the digestive and respiratory systems work.
While people born with CF now can expect to survive in to their 40s, the average age of death is currently 23.
GOSH researchers plan to use a vector - such as a non-infectious virus - which can take a healthy copy of the gene into the lung cells of children with the condition.
Dr Adam Jaffe, who is leading the Great Ormond Street work, said there were important issues to consider when deciding if such trials should be permitted - but children's health was at stake.
"We could be denying children life enhancing treatment on inadequate grounds.
"There are scientific and medical reasons why the treatment might work better in children.
"The main aim is to halt the decline in lung damage, which begins soon after birth so it makes sense to start treatment in early childhood.
"Children are not little adults; and this is particularly true in cystic fibrosis."
He added: "It is possible that if the gene therapy trials were carried out in adults we would not see a benefit as the mucus in the lungs of adults may act as a barrier and stop the gene from getting in.
"Furthermore, inflammation can be more serious in adults so they may suffer more severe side effects from some vectors which help to get the gene into the cell.
"There is evidence from other research that gene transfer may happen differently in growing and adult lungs"
A spokesman for the CF Trust, which is planning its own gene therapy trial, said: "As cystic fibrosis is a progressive illness we recognise that it is necessary for gene therapy trials to be conducted on those who will receive clinical benefit.
Professor Eric Alton, of the UK Cystic Fibrosis Gene Therapy Consortium, said studying patients over 12 was a balance between patients being too young - with healthy lungs where you could not see a difference after treatment, and being too old - where their lungs would be in too poor a condition.
He said there was probably an "optimal window" where testing would show reliable results.