For one thing, as Krisken pointed out, to keep businesses from hiring teenagers who cost less than minimum wage required for adults to do drudge work instead of those adults.Why exactly do they deserve to get paid the exact same hourly wage as adults who need the job to keep a roof over their head and food on their table?
Also, are lunch breaks not part of the law where you are? They are in NJ/NY. You cannot legally prevent someone from taking 30 min during their work day for lunch.
EDIT: Totally ninja'ed by Krisken.
EDIT2: Correction, NY has break laws, but NJ does not if you're over 18.