Most full size cribs have 4 height adjustments. The first and highest setting can be used when the baby is newborn and there is no rolling over or pulling up on the rails. Once the baby begins to become more active, this is when the mattress support should be lowered to either the second or third setting depending on how active the baby is. Once the baby is crawling and standing we suggest the lowest setting. Some babies learn to climb quickly, once they do we strongly encourage this to be the time to use the toddler rail kit.
If your child is tall and the chest meets the lowest crib side rail, or they are 35" in height the child will be able to climb and possibly fall out of the crib, as the parent, please use your best judgement as to when it is an appropriate time for your child to move on to the next sleeping stage or full size bed conversion.
And for no reason should the crib be used as a play pen or place to keep your child enclosed and out of the way. The crib is for sleep only.
Our cradles do not have adjustable mattress support heights. Once a baby begins to become active and can roll over on it's own, this is the time to move up to the crib!