Some mental health trusts in England have seen "no significant investment" in psychiatric services for children despite government plans to overhaul provision, say experts.
Last summer ministers said they would invest an additional £143m in the services this financial year.
The Mental Health Network suspects the funding has been used to support other NHS services.
NHS England says it can show where the money has been allocated.
The additional funding was part of a £1.25bn investment over five years announced by the chancellor in the Budget in March 2015.
While campaigners expected £250m to be made available this year, the Department of Health said in August that only £143m would be spent, as providers did not have the capacity to spend any more.
However, the body representing mental health trusts says it has seen little of even that reduced amount.
How the £143m was allocated:
- £75m - Clinical Commissioning Groups
- £21m - Health Education England
- £15m - Perinatal care (£11m underspend)
- £12m - Improving Access to Psychological Therapies programme
- £10m - Hospital beds
- £5m - Administrative costs for NHS England (£4m) and Department of Health (£1m)
- £2m - Improving care for young people in the justice system
- £2m - Joint programme with Department for Education to improve services in schools
- £1m - Support for children with learning disabilities in long-term care
Source: NHS England
Stephen Dalton, chief executive of the mental health network which represents NHS providers, said: "Providers of mental health services and most importantly children and families are struggling to see the difference.
"It doesn't seem to have turned into posts on the front line. We are not hearing any reports of any significant investment at a local level around children's services. Indeed, some services are still experiencing cuts in services."
NHS England says it has provided £75m to clinical commissioning groups (CCGs), but NHS providers fear some of the money has been siphoned off to pay for other services.
Acknowledging that is a possibility, CCGs have told BBC News they want NHS England to ring-fence the money, specifically for children's mental health services.
Dr Phil Moore, chairman of the NHS Clinical Commissioners Mental Health Commissioners Network, said: "Despite our commitment to better mental healthcare for young people, it has to be acknowledged that CCGs are dealing with increasingly financially challenging times and a myriad of competing demands on budgets.
"This, combined with the fact that children and young people's mental healthcare is in desperate need of heavy investment having historically been treated as a 'Cinderella service', is why we believe this is a rare case where funding should be ring-fenced."
Some trusts say they have seen additional funding - the South London and Maudsley, for instance, said they had received an additional £1.8m from four separate CCGs.
And several CCGs told us they were committed to spending the money on new services.
But some children's mental health services are also being cut, especially those provided by councils.
Dr Marc Bush, senior policy adviser at the charity Young Minds, said: "Our expectation is that overall spending on children's mental health services this year may either be flat or fall slightly in real terms."
Former care minister Norman Lamb, who helped secure the extra funding, said he was concerned about the lack of progress.
"Given the pressure on the whole system including local government, there is a real risk that funding intended for children's mental health ends up elsewhere or simply replaces other funding cuts.
"There is an absolute moral imperative to address the very serious underfunding of children's mental health. Failure to invest this money now would be unforgivable."
An NHS England spokesman said: "As a society we must make sure the most vulnerable children get the very best care as quickly and simply as possible and that they are being offered the right services in the right places. But transformation will not happen overnight.
"Every CCG has worked with local partners including children and young people to deliver plans to improve access to effective services."
The Department of Health said that an additional £250m would be invested in children's mental health services in the next financial year.
NHS England says £89m will be allocated to CCGs, but the money has not been ring-fenced.