Many NHS trusts have significant flaws in the service they provide for children, a report finds.
Millions of children are treated in hospital each year
The Healthcare Commission found that overall the quality of child services in NHS hospitals in England was good.
But day care and emergency care were both found lacking in 28% of trusts, and outpatient care was rated as weak in 46% of trusts.
The commission was assessing progress towards implementing national standards in 157 hospitals across England.
The standards were set out in the government's 10-year National Service Framework for Children and Young People, launched in 2003.
Among the key recommendations were that children should be treated in a child-specific and child-friendly environment, and sufficient staff should be trained in the care of children.
Overall, a quarter of trusts assessed received a rating of "excellent" or "good", 70% were rated as "fair" and only one in 20 was rated as "weak".
However, the commission found problems in a significant number of trusts when it considered individual departments in isolation.
Outpatient services had the greatest room for improvement, with many trusts having particular problems providing sufficient staff cover with the right expertise, such as children's nurses.
The same problem was found in many A&E departments, where many trusts also struggled to provide child-friendly environments, often forcing children to use facilities open to all ages.
This is despite the fact that up to 25% of the child population - around 2.5m children - are seen each year in A&E departments.
In addition, 28% of trusts scored "weak" on training for staff in emergency surgery, and 22% of trusts scored "weak" in elective surgery. None scored good or excellent in either category.
In contrast, 71% of trusts scored "good" or "excellent" for in-patient services, which were most likely to have appropriate staff cover and training, and where children were most likely to be treated in child-only wards.
Anna Walker, the commission's chief executive, said: "Some of the findings in this review are very encouraging, especially the "excellent" and "good" scores of so many hospitals and the success of inpatient wards in providing child focused healthcare.
"However, the problem areas seem to be accident and emergency, and outpatient services. More skills in dealing with children are needed here.
"Children's healthcare is very distinct. It has real needs of its own and is not the same as adult care."
The commission has sent detailed reports to every trust it assessed, and is working on action plans for those where performance was weakest.
The review of children's services is the first of four assessments which will form part of the commission's new system for assessing NHS performance.
Jo Webber, deputy director of policy at the NHS Confederation which represents NHS organisations, said: "It is encouraging to note that only 5% of trusts were given a weak rating and I'm sure that these organisations will now be looking to see where they can make improvements."
Dr Patricia Hamilton, president of the Royal College of Paediatrics and Child Health, said: "Children's services have been under-funded for a long time.
"Insufficient emphasis has been placed in the past on making the environment child-friendly and there is increasing pressure on A&E services as parents opt to take their children to hospital rather than to their GP."
Dr Sheila Shribman, the "Children's Tsar", said the results were encouraging, but there was still room for improvement.
"Although only 5% of trusts were rated as weak, we shall also be looking to the 70% of trusts rated as fair to see where standards can be further improved - to rate good and excellent," she said.