The hospital, run by Cygnet Health Care Limited, has changed its use since the inspection and now only provides services to adult male patients.
The report, after a CQC visit to the 43-bed mental health unit in July, said inspectors reviewed CCTV footage for three cases of restraint where children were physically abused by staff.
"Staff were observed dragging children and young people during these incidents," they said.
"For all three incidents reviewed, there was no apparent risk requiring restraint presented by the young person."
They added there was no evidence of staff trying to de-escalate the situation before restraining the children.
The report said footage identified 12 members of staff as "passive bystanders" who did not raise concerns.
Four out of seven children they spoke to said they "did not feel safe at the service".

