We tried to let Heidi Anne sleep in her crib as a toddler bed, however, it didn't have any railing. To make it safe we put her play mats under the crib. We put her into bed and she promptly rolled off the bed head first. She looked at us shocked at first, then giggled. The second time we put her further from the edge. She rolled off with momentum that time, fell, and again giggled.
It was a losing battle from there.
She would crawl up into her bed, fall off (each time in a different way, head first, rolling off, leaning over, whatever her little 1 year old mind could think of), smiling the whole time she was falling, and giggle at the landing.
We gave up, let her have her fun for a bit, then put the crib railing back on. When we put her back into bed, she rolled against the railing (always testing the boundaries) hit her glow worm and fell asleep.
I think we'll get a real toddler bed with safety rails this weekend.