DD was 16months old. She had previously gone to bed pretty much no hassles and self settled, when all of a sudden she started having these huge hissyfits everytime we took her near the cot.
Took me about a week to figure out that she just didn't want to sleep in there. Preferred even the floor to the cot.
On a hunch I borrowed a foldup bed from my mum and voila! A sleeping child.
We were moving a month after that so she slept on the fold out until we moved (600km) and then we just bought and put her new bed into her new room. She went straight onto an ensemble of regular size, but as she had co-slept for a long time she was aware of the edge of the bed and so never fell out even without a bed rail.
Many suggest getting them to pick their own linen etc but at that age she was too little - heck she still doesn't particularly care now.

DS went into a bed before he was 1, though due to the age we put a bed rail on. He has never slept in a cot and always slept with me (this must be prefaced with has always refused to go anywhere near the cot). He's never even really looked like falling out but he's still so little.