Elders should mind their own business.
Parents should mind their children.
If the teens are involved in (borderline) illegal acts, or hanging with bad people (bad as seen by worldly people, not as seen by JW), or similar potentially self destructive behaviour, probably the parents should be made aware.
If the teens are just not following all man-imposed JW rules, let them be.
Oh, did I mention elders should mind their own business?