Not guaranteed. However, when we didn't get the King we'd requested, we were upgraded.
We did not request bunk rooms for our May trip, but evidently the CM making our reservation had noted that we'd be traveling with 3 children (1 under 3). He had placed a bunk request on our reservation. We spent our first night in a standard view room and our second in a savanna view room and had bunks both times. The resort was completely full during part of our stay. (I know this because of a conversation I had with a CM when I tried to add-on 2 more days and not even a suite was available!!)