Police officers running cadet programmes in London and Manchester are under investigation, accused of abusing their position for a "sexual purpose".
The Independent Office for Police Conduct (IOPC) has demanded an urgent review of cadet training as a result.
Two constables, one in each city, are subject to criminal investigations.
Four more officers, three with the Met and one in Greater Manchester, are being investigated by the IOPC over how they dealt with the reports of abuse.
The Greater Manchester Police (GMP) constable has been arrested and released on bail and more potential victims have been identified, the IPOC said.
A spokesman said: "The allegations can be broadly characterised as abuse of position for sexual purpose."
The conduct of a police sergeant is also being examined, regarding how they dealt with the reports of alleged abuse by the PC.
'Serious and sensitive'
The Metropolitan Police confirmed one of its constables had been suspended and was the subject of a criminal investigation following allegations he abused his position for a sexual purpose at a London-based cadet training camp.
The IOPC has received a referral from the Met in relation to "potential failures" by three officers - an inspector, sergeant and PC involved in running a cadet programme in the London region - to put in place immediate and appropriate safeguarding arrangements after being made aware the abuse may have taken place.
Both investigations are at an early stage and involve "serious and sensitive allegations", the IOPC said.
IOPC deputy director general Ian Todd said: "We are sufficiently concerned by these two referrals to ask all police forces in England and Wales to urgently review their own volunteer police cadet programmes to ensure they have robust safeguarding procedures in place."
He added: "I must stress that the two investigations are unconnected and we have no information to indicate this may be a wider problem," Mr Todd said.
"However, some of the evidence emerging from these investigations indicates that there may have been opportunities to act sooner on the allegations that we are now investigating."
Commander Mark McEwan, who leads for the Met on crime prevention, inclusion and engagement, said it was hugely important the highest possible safeguarding standards were followed at all times when officers had "direct contact with the young and the vulnerable".
He said: "Following these allegations, the Met carried out a full review of safeguarding and vetting in relation to the VPC programme and meetings have been held with all VPC coordinators and supervisors about their safeguarding responsibilities, and compliance with policy.
"Each Met borough has a dedicated programme coordinator assigned to it - something unique to the MPS - and all adults who work on the VPC programme have been subject to enhanced vetting checks, and receive additional safeguarding training."
A Greater Manchester Police spokesman said a review of its cadet scheme had identified where safeguarding measures and training could be enhanced, and said reviews and development would be ongoing.
NSPCC public affairs manager Andrew Fellowes said: "Strong safeguarding arrangements are crucial in any organisation and these investigations in relation to police volunteer cadet programmes for children are very concerning."