This is true anytime you leave and return, not just from a tour. Kids don't need a photo ID - I believe the cutoff is anyone 16 or older needs a photo ID. Actually the photo ID is normally shown to port security and not the ship's security.
When you embark on your cruise they will take your photo at a security station and match it to your cruise card via a card reader. Whenever you exit or return from the ship you scan your card and your photo appears at the security station so they can verify it is you. This also ensures they know who is aboard, who is ashore, and who missed the ship's departure.