Last jan I had a 21 month old start and he too could get out of the play pen. My dcks sleep in my bedrooms so I left the door open a crack so I could see him and as soon as he swung over I open the door quickly to startle him and with my mean face I said "no climbing out"! And then I put him back in .... Rinse and repeat .... After two weeks he never climbed out again !!!