Without specifics, it's hard to know how egregious this is. For instance, did multiple 15 year olds work until 7:15 PM on a school night instead of 7:00 PM? If so, that's not really "exploitation" in my mind. However, if there's an ongoing issue with 14 and 15 year olds working till midnight, working 12 hour days, or something similar, then I would agree that the fine is pretty light.