Mommy 22 ... As soon as i would hear the baby get out the the play pen I would go in with my mean face and say " no climbing out" and put himback in and keep doing it till he stays there .... I had one start with me at 21 months doing the same thing and after a couple if weeks he never got out again and is my best sleeper. Even if nap time was over and he climbed out I would put him back in and leave for a few minutes then go in and get him .... That way he knew even if he was awake he was never allowed to climb out he had to wait for me