transition

transition, noun: passage from one state, stage, subject, or place to another

I walked into the baby's room to find him standing up in his crib, the railing height of which is lower than his waist!  Time to lower the crib mattress so he doesn't fall out.  Additionally, I found a rip in my daughter's toddler bed mattress, so now she needs a new mattress.  And since we don't want to buy another toddler mattress for her, we're just going to get a full sized mattress and transition her to her bigger big girl bed.  Not like that matters, she sleeps on the floor most of the time anyway!