My daughter was able to lift her leg over the top of her crib at 18 months, so we had the concern of her climbing out (she never actually did), so we put her in a toddler bed a few weeks before moving. When we were packing to move, we just told her that the crib was staying at the old house and she was a big girl in her big girl bed. We moved and she transitioned well to the toddler bed, and within a couple weeks, she started waking up multiple times a night. One night, I went to check on her and she was sideways in the toddler bed with her leg stuck between the bed and the rail. We figured out that she was waking herself up because she didnt have enough room to move in her sleep. Her grandparents gave her a set of bunkbeds, and we took her to pick out new sheets, got them set up and she helped up get rid of the frame and said bye to the mattress (we sold it on Craigslist as it was only 6 months old!) and she slept through the night that night! She is 6 now, and still sleeps in the bunkbeds, but really wants a regular bed!