The number of under-18s admitted to adult mental health wards or treated on them is rising, figures show.
Despite government pledges that the practice would be stamped out by 2010, more children spent time on adult wards in the first eight months of 2013/14 than the whole of the previous year.
England-wide data from the Health and Social Care Information Centre (HSCIC) shows that from April 2013 to November 2013, 250 under-18s spent time on adult mental health wards.
There were also 303 admissions for under-18s to these wards, and they made up 10,424 "bed days" in the units.
This compares to 219 under-18s spending time on adult mental health wards in the whole of 2012/13 and 236 admissions.
Previously, the number of under-18s being treated or admitted to adult mental health wards had been falling.
The latest report said: "The figures for people and admissions is already higher than the annual figures for 2012/13 even though they only cover the first eight months of 2013/14 and the figure for bed days is close to the level in 2012/13."
In 2011/12, 357 under-18s were treated on adult mental health wards in England, which fell to 219 in 2012/13. For the eight months of 2013/14 alone, the figure reached 250.
The number of admissions among under-18s fell from 440 in 2011/12 to 236 in 2012/13, but rose to 303 for the eight months of 2013/14.
Care and Support Minister Norman Lamb said: "Children and young people should not be treated on adult mental health wards. Our mental health crisis care concordat makes clear that the NHS must treat people under 18 in an environment suitable for their age, according to their needs.
"We've also invested £54 million to transform services, giving children and young people improved access to the best mental health care."
Lucie Russell, director of campaigns and media at the charity YoungMinds, said: "The legislation clearly states that an adult mental health ward is not an appropriate setting for vulnerable children with mental health problems.
"Urgent action must be taken to ensure that the worrying increase in children on adult wards is halted and that both early intervention and crisis services improve."