Following the initial dispositional order issued pursuant to N.H. Rev. Stat. § 169-B:19 regarding a charge or charges arising out of a single incident, a child shall not be securely detained for a period or periods totaling longer than 21 days while awaiting placement or a hearing regarding a change of disposition, or for any other purpose. The court may permit extended detention beyond this limit if it finds by clear and convincing evidence that extended detention is necessary for the safety of the child or the public and the child consents with the assistance of counsel. In any case involving a child who is detained, the court shall ensure that the child is continuously represented by counsel during any period of detention. In cases where extended detention is permitted pursuant to this section, the court shall hold review hearings with the child and counsel present on a weekly basis to determine whether detention continues to be justified.