Children (under 18) need their original certified birth certificate TO BOARD only. After that, I put it in my "documents" stuff and basically never get it out again. On the ship, everyone needs only their KTTW card.
To get on and off the ship at ports, children need only the KTTW card. Adults need the KTTW card AND a photo ID.
There is no need for any school ID or anything like that. No one carries around birth certificated, and no one needs a photo ID on the ship. THe only time you might need the birth certificate again is IF US Customs requests an additional document check at Key West, St. Thomas, or back at Port Canaveral. This is not the usual, but with the heightened security alerts, we have on occasion had extra document checks. These are handled in the theatre before anyone is allowed off the ship.
DCL makes it as painless as possible, and you can return to your cabin after the check to put your documents back in a safe place.
Kids get a name tag when they register for the club. THe name tag has a place to store the KTTW card. When a child checks into the club/lab, the counsellors take and file their KTTW card. THey get it back when they leave the programming each time--so the counsellors have the cards ONLY of those children under their care at that time.
Hope this clears things up.