On the Disney ships, after you lock the door, there is a second lock that you need to twist that is located about 5 feet high on the door. So, the child would need to climb on the sofa or drag the coffee table over, climb up to twist that knob in the correct direction, then climb down and swivel the door handle downwards then pull the sliding door open. That would get him access to the verandah.
Once on the verandah, he would need to drag the deck chair over to the verandah railing, the climb up and onto/over the railing.