One critical factor used to consider whether your child is ready for a “big girl” or “big boy” bed is if they are saying they want one. Often it seems it’s the parents driving the readiness train and not necessarily the children. It’s better to be a little late in the game than too early when it comes to sleeping in a bed. Why? Because if they are too young, they won’t have the cognitive ability to understand staying in their bed all night or all nap, which means Mom or Dad are now dealing with that issue.
I often hear from parents who moved their little ones into a bed hoping it would promote better sleep. It's extremely rare that moving a child who doesn't have good habits in their crib will suddenly jumpstart them into sleeping better in a bed. Instead, consider establishing healthy habits in the crib first and then watching for readiness of a big kid bed.
Don’t be misled into thinking you must go from a crib to a toddler bed – a smaller bed that uses a crib-sized mattress. We used a double bed that has lasted into the teen years (with a new mattress along the way, of course). It has experienced many incarnations (not including the ones from its former owner), from a bright yellow little boy’s bed to a turquoise blue little girl’s bed to its current state as a bohemian teenager’s bed. I enjoyed snuggling into a spacious bed for bedtime reading and cuddles as part of the nightly routine, which will work even with a regular-size twin.
When the time is right for your little one, you have a couple of options for making the transition to the new sleeping arrangements. One is cold turkey: Remove the crib, replace it with a bed and you’re ready to go. You may want some floor padding or a bedrail if you’re concerned of falls, but that is optional, especially if the bed is low to the floor, which I recommend.
The other option is a gradual approach: Begin with the railing down on the crib. If both crib and new bed fit into the room at the same time, you can begin bedtime routines (reading, cuddling) on the new bed before moving to the crib for sleep. Once your child is sleeping in the new bed for both naps and bedtime, remove the crib.
The privilege of sleeping in a big girl or big boy bed comes with rules – primarily, staying in bed during sleep times. It’s important to be consistent with this from the get go, or you’re likely to have a roaming toddler on your hands.