Mine both decided that the best way to learn to get out of their cot was to get their hips up against the side, all pressure on their arms and then tip forward headfirst onto the floor. In both cases a mad scramble for a toddler bed and teaching them to stay in their bed at <2 (a hopeless cause resulting in soft floors and a tall stair gate on the door) resulted

By three in both cases they were in full size singles for different reasons and so far there they stay (8 and 4 currently)