More than 150 paediatricians are calling on the government to scrap its controversial Health Bill, saying it will have an "extremely damaging effect" on the health of children.
In a damning letter to The Lancet medical journal, members of the UK's Royal College of Paediatrics and Child Health said there was "no prospect" of improving the Health and Social Care Bill, currently going through Parliament.
And they accused the Government of "misrepresenting" the Bill as being something that was necessary for the NHS.
The signatories join several Royal Medical Colleges, including the Royal College of GPs and the Royal College of Radiologists, in calling for the Bill to be scrapped.
The move will put increasing pressure on the Government over the reforms, which have come under repeated fire from healthcare professionals.
Unions, including the British Medical Association (BMA), the Royal College of Nursing (RCN) and the Royal College of Midwives (RCM) are among those calling for the Bill to be withdrawn.
Today's letter said that "if passed, we believe that the Bill will have an extremely damaging effect on the health care of children and their families and their access to high-quality, effective services".
It added: "We see no prospect for improvement to the Bill sufficient to safeguard the rights of access to health care by children and their families.
"In our view, no adequate justification for the Bill has been made.
"The costs of dismantling existing National Health Service (NHS) structures are enormous and, at a time of financial austerity for all public services, have resulted in precious resources being diverted to private management firms and away from frontline patient care.
"We believe that the Bill will undermine choice, quality, safety, equity, and integration of care for children and their families."
The signatories said the NHS already "outperforms most other health systems internationally and is highly efficient" and expressed fears over the potential role of private companies in managing groups of GPs, who will control most of the NHS budget, under the new system.
They added: "Competition-based systems are not only more expensive and less efficient but are associated with gross inequality in perinatal and child health outcomes, including child safeguarding.
"Far from enabling clinicians to control and determine local services, the new commissioning proposals are more likely to lead to increased power for private management organisations attracted to this lucrative opportunity to manage small Clinical Commissioning Groups."
The letter said using multiple private companies "will make it difficult to innovate, co-operate, plan, and improve the quality in children's services".
They warn care will "become more fragmented" and families and clinicians will struggle to organise services for children.
"Children with chronic disease and disability will particularly suffer, since most have more than one condition and need a range of different clinicians.
"If different services are commissioned from separate providers, this risks the breakdown of the relationships that underpin good communication and co-ordination, particularly where different aspects of service are provided from different budgets."
Safeguarding of children will "become even more difficult" when services are put out to competitive tender and organisations "compete instead of co-operate".
"Children who are vulnerable, neglected, or abused will inevitably slip through the net."
The doctors argue the Bill is "misrepresented" by the Government "as being necessary and as the only way to support greater patient choice and control".
"On both counts that claim does not stand up to scrutiny.
"Far from increasing choice, there is plenty of evidence amassing that these proposed reforms will in fact limit choice for all children and their families, increase inequalities, and harm those who are most vulnerable.
"Continuous quality improvement in our already high-quality NHS does not require this legislation."
In recent weeks, the Royal College of Psychiatrists and the Chartered Society of Physiotherapy (CSP) have called for the Bill to be withdrawn, while the Royal College of Anaesthetists and the Royal College of Physicians say they still have major concerns.
The Royal College of GPs, which represents more than 44,000 doctors, said the reforms would "cause irreparable damage to patient care and jeopardise the NHS".
More than 130,000 people, including footballer Rio Ferdinand and TV star and author Stephen Fry, have signed an e-petition calling for the Bill to go.
Earlier this week, the Prime Minister said he was "at one" with Health Secretary Andrew Lansley over the reforms.
Liberal Democrat deputy leader Simon Hughes has said Mr Lansley should "move on" from his role after NHS reforms are completed.
A spokeswoman for the Department of Health said: "We have listened and substantially strengthened the Bill following the listening exercise.
"It's not true to say that the Health and Social Care Bill will fragment children's healthcare.
"In fact, the Bill will help address the very concerns about fragmentation that the experts raise.
"It will help the NHS and other public services work together better for children, young people and their families.
"These 150 individuals represent just over 1% of the total members of the Royal College of Paediatricians and Children's Health and cannot be taken as an accurate representation of the College, who we continue to work with."
Shadow health secretary Andy Burnham said: "Warnings for ministers do not come any more serious than this one.
"The government is being told in no uncertain terms by 150 experts that it is putting children's safety at risk with its reckless NHS reorganisation. By pressing on, it is putting its political pride before what is best for children.
"It is simply outrageous for the government to gamble with children's safety and this warning is sufficient reason alone to drop the Bill.
"Ministers can't simply ignore it as it backs up similar warnings revealed earlier this week in risk assessments by NHS bodies."