[ThorinJacobs]

+1 On this, and I'd want to encourage them to provide this feedback throughout the internship as well, not just at the end. Sure, sometimes they'll have suggestions that we've considered and decided not to do, but if it's a common question we should document.

For helping the interns, I'd talk to them about what they learned, what their next career steps are, and what subjects they're most interested in. Ideally, you have a mentorship program setup already where this has already been discussed, so this may end up being very brief. But even without a mentorship program, having good discussion about how you can help the interns aside from just having an extra line of experience on the resume is healthy for both sides.

For improving the program for future interns, I'd also ask them what they wished they knew when they first started their internship. For all of the above, make sure that it's a safe environment to have honest discussion - for instance state outright that they're not going to burn bridges by pointing out process flaws or talking about working at other companies in the future.