I'm not totally certain how it is at AKL but at other deluxe resorts there is only a limited supply of actual cribs. You could get one, but most folks will get a pack-n-play.
You can call at any time and add it to your reservation.
In my experience, don't be too alarmed if it's not in the room when you arrive or otherwise not brought to you without you having to give them a friendly reminder nudge. I would recomend either calling housekeeping from your room (don't call the front desk) or physically ask at the front desk.