Thousands of disabled children are waiting too long for vital treatment because of cuts to services, a survey suggests.
The British Academy of Childhood Disability (BACD) says some are waiting more than two years for a diagnosis.
Dr Karen Horridge, who chairs the BACD, says children with autism and complex disabilities are being failed.
The Department of Health said it was working to help join up health, education, and social care services.
Dr Horridge, who conducted the survey, said the delays in assessment and eventual diagnosis “were unacceptable”. She told BBC News that these children were missing out on vital therapy and support because of these delays.
In some cases, they could miss out on years of education.
She said: “They’re left in pain for longer. They’re left with difficult behaviours for longer, and then things become very much more complex to unpick by the time we do get to see them.”
The survey contacted 200 paediatricians who lead child development teams across the UK.
Of the 134 who responded, more than a third said their teams had been cut by up to 20%, and nearly three-quarters said waiting times had increased.
One paediatrician, who did not want to be named, told the BBC they were under pressure from managers to “fiddle” waiting times.
The doctor described routinely returning referrals to GPs before registering them formally, which would delay the child’s care, to meet 18-week referral targets.
Of all the doctors who responded to the survey, 80% said they could not meet guidelines set by health watchdog the National Institute for Health and Clinical Excellence (NICE).
Child-development teams are in place to support those from birth to 19 who have a range of different neurological disabilities such as autism, cerebral palsy and epilepsy.
Often the disabilities are complex and can affect the child’s speech, memory, language, sight and hearing.
It took more than a year for seven-year-old Ruby Fisher to get the support she needed.
After many months in pain, struggling to walk, she was finally diagnosed with hypermobility, which affects the joints and can cause dislocations, stiffness, fainting and extreme tiredness.
She would often fall over and could not eat or write without help.
Her mother, Debbie Fisher, said she had cried in relief when her daughter had finally been diagnosed.
“She was in constant pain, she used to complain about it everyday,” she said.
“I feel annoyed we were left so long. I feel like if a little bit more care was taken, maybe if somebody could have helped, we could have got here a lot quicker and avoided so much pain and upset over the years.”
Now Ruby has had her appointments with the physiotherapist and occupational therapist, she is able to do a lot more.
She can run, her writing has improved, and she feels like she is able to keep up with the other children.
Mrs Fisher added: “Since the appointment, we have been given aids and ideas to help my daughter in day-to-day activities.
“It’s given her a little bit of independence back.”
Responding to the survey’s findings, the Department of Health said there had been an increase in the numbers of paediatricians employed but it could not say whether these were doctors specifically for children with disabilities.
The department added: “Children with learning disabilities deserve the best possible care and a timely diagnosis.
“Decisions on spending are made locally, but we are working to help join up health, education, and social care services to make sure they get the care they need as quickly as possible.”