Cribs are the home base, fort, security, battleship, starship, boat, prison, and comfort all in one place. So when should a toddler 'graduate' from crib into a toddler bed? There are some clear do's and don'ts when it comes to this transition.
Children that are between 1 1/2 and 3 years old are usually ready to move from a crib to a toddler bed. Potty trained children benefit the most from the transition because they can get in and out. The transition straight from a crib to full sized bed would most likely be too large of a change for two reasons: toddler beds have safety rails for the 'active' sleepers and children generally feel safer in a smaller bed. The transition to a full sized twin should come later as the toddler outgrows his/her small bed.
Baby Beds
Since most kids don't have very much choice in matters (i.e. food, clothing, bedtime, bath etc.) it is highly recommended that the child is given full choice in this simple matter. A toddler that gets to choose when to move to a bigger bed and how it should look will feel immense pride in themselves. So talk to your child about getting a bigger bed and what kind of fantastic new kids bedding they could have on it for a few weeks ahead of time. They'll get used to the idea and hopefully get excited about going to the store and helping pick out their new bedding.
Put the toddler bed in the same place that the crib was located. Continue encouraging your child and playing up their new bed even if they take to it just fine. If the child doesn't like the new toddler bed it is no problem to let them go back to their crib-some children just don't like change. Just try to build up the excitement again and try to introduce it at a later time. If the child wants to keep their old nursery set, let them.
Never make multiple changes to a toddler's life or schedule at one time. If they are potty training, or moving, or welcoming a sibling, or dealing with a new babysitter, or experiencing another change let them first settle into a quality routine. Don't rush your child. Forcing them to be a 'big' boy or girl could be dangerous if they aren't ready because they could fall out or get out in the middle of the night and make mischief when everyone else is asleep.
Finally, a toddler bed is better than a new bike or big toy because they use it every day for a long time. The toddler bed should be of high quality and fun. Put some thought into making it welcoming and fun. Who knows, your child might even be willing to go to bed at their scheduled time.