We were always allowed to take any dish or cup or glass from any place and walk it around the ship, kids cups from MDR are no exception. IDK if it was a supply issue or some other reason but our December cruise did not have the same cups as the two prior we had been on. In February we received clear plastic cups with domed lid that are quality enough to be re-usable and even souvenir worthy. (Side note, in a restaurant I've worked at the kids cups were plastic and thrown away after each use, anyone know if
DCL re-uses theirs?). In December we received what were more the quality of to-go cups and not something I would keep to use around the ship.