I served as an intern in high school, and I thought it was a good experience. I had the chance to work for two different industries, computer science at a bank, and an assistant to an orthopedic surgeon. In both cases I didn’t really do any work that matters, but I had the chance to see how the businesses worked, and it helped me to decide how I wanted to proceed in my career.
In college I actually had a paid internship, alternating a semester of work with a semester of college, and that was more like a real job.
I think internships are a great way to teach someone a bit about your business, and also to find potential employees down the road. It isn’t a direct investment, and I’d guess that for every 10 interns you had over time, you might find one or two that would make good employees, but it’s a good service to the community and for younger people, and it gives you a chance to see how interesting your work is to others. You might even learn a thing or two from a fresh set of eyes.
However be careful, and don’t treat interns as free labor, to be exploited. Make sure you follow the guidelines from the US DOL.