I mean, I used to worry about scratching them, but a microfiber cloth dampened with lens cleaner works best. Idk, maybe it's just me, but wiping in one direction from the center out keeps it safe.
He kept messing with my tools, so I sat him down and showed him how to check the mirror in an SLR. Now he points out when one looks off, and it's cool to see him pick it up.