The centerpiece exhibit in Portland’s kids’ museum is its camera obscura, a room-size “camera” located on the top floor of this stout, columned downtown building next to the art museum. Children gather around a white table in a dark room, where they see magically projected images that include cars driving on city streets, boats plying the harbor, and seagulls flapping by. This never fails to enthrall, providing a memorable lesson in the workings of lenses. That’s just one attraction; there are plenty more, from a simulated supermarket checkout counter to a firehouse pole to a mock space shuttle that kids pilot from a high cockpit.