The letter does not name another officer who initially accused the teenagers.
The family of one of the teenagers says that accusation was made without any evidence.
That officer is still serving as a police officer in Central Otago.
A parent of one of the teenagers said the teenagers and their supporters were grateful to Mr Kerrisk for resolving the issue once it came to his attention.
In the letter, Mr Kerrisk said the families had not received the ''level of service or treatment from police staff that you deserve''.
''You outlined in your concerns that you had been blamed for [incidents of petty crime] and had been targeted [by police] since then.
''I have spoken to the officers, and [name of police officer] has acknowledged the incident of an altercation [with one of the teenagers].
''He expressed regret that they [that and other incidents] had occurred but explained it was an 'old-fashioned policing style' that he had.''
Two other teenagers have since been found to be responsible for the petty crime.
Southern district police would not provide any further comment, other than to say police had worked to resolve the original concerns raised by the teenagers and their families, who could make a formal complaint either directly to police or via the Independent Conduct Authority if they had continuing concerns.