Definitely they should be paid. If they work for free, then people with money again have a large advantage over families that don’t. If a student has to work to pay for their education then they can’t do an internship. Kids like me, where my parents paid for my education, I could have done whatever I want (I wish I had taken advantage of that) to increase my experience and resume.
Moreover, well established companies with a lot of presence wind up getting the best free labor, again putting the people (or company in this case) with an advantage over the small businesses, which gives them a competitive advantage in cost of goods sold, in turn giving them a pricing advantage selling their product or service.
I’m fine with paying interns less, because training them takes time, but I’d go with paying them about 75% of what someone gets paid in the job they do, or the lowest amount in that pay band put forth by the compensation rules in the company. Usually, a company has a range for a job. A CAD designer might make anywhere from $15—$25 an hour at the company, so the interns would make $15.
If the intern is working in marketing, but their basic job is administrative, they should be paid similar to an admin, even though they are really interning to learn about the marketing job of someone higher up.
Edit: I wanted to add that even though I could have worked fir free as a student, I feel pretty sure I would have felt taken advantage of doing it. I’m guessing within a month’s time I would be fed up.