The police watchdog has studied another 13 cases of child strip searches by Metropolitan Police officers in the wake of the Child Q scandal.
The Independent Office for Police Conduct (IOPC) said it was so concerned by the force's delay in passing on the details, it would examine more cases to see if they were being handled properly.
Four Met officers are facing gross misconduct charges over Child Q, a 15-year-old black girl who was strip searched at her east London school on suspicion of carrying cannabis in December 2020.
The incident was widely condemned, with Child Q having been on her period and left traumatised.
No adult was present during the search by two female officers, and her parents were not called at the time. No drugs were found.
The IOPC has issued the Met with recommendations to ensure that when they consider a strip search, officers prioritise the child's safeguarding needs and best interests, conduct it in the presence of an appropriate adult, and maintain the child's dignity while considering their health, hygiene and welfare needs.
The watchdog said that in the majority of cases it examined, no appropriate adult was present. In nine of the 14 cases, nothing suspicious was found in the strip search.
IOPC director general Michael Lockwood said: "We have been concerned about what we have seen in the cases referred to us involving complaints about strip searches of children, and we are acting now by making recommendations stressing that existing best practice and policies should be followed by the MPS at all times.
"Given the apparent delay in some of these cases being referred to us, we will now work with the MPS to review a sample of complaints that have not been referred to us, to establish whether the process is working as it should."
The recommendations are being issued to all police forces in England and Wales, and chief constables are being urged to make sure correct procedures are followed.
The Met described what happened to Child Q as "truly regrettable" and has apologised publicly to her, her family and her community.
Deputy assistant commissioner Laurence Taylor said: "Ensuring the safeguarding of every child who is subject to a search is an absolute priority.
"What happened to Child Q was a truly regrettable incident, and we have apologised publicly to her, her family and the wider community. We understand how much concern this incident has caused, and how distressed Child Q has been."
A review of the Child Q case by Jim Gamble of the Independent City and Hackney Safeguarding Children Board said the girl should never have been strip searched and found failings by police and her school.
The review also found that "racism – whether deliberate or not – likely played a role in what happened".