Request it on your reservation and also check in as early in the day as you can. There is no guarantee, though. Of the 2 times we requested connecting rooms, once we got them and once we didn't. The time we didn't was at Caribbean Beach and the CM said there just weren't many people checking out that day and they couldn't get rooms together. They did give us rooms that were one apart. They also could have moved us to connecting rooms the next day, but our things would have needed to be in storage during nap time, which didn't work for us.
And, yes, the beds are kinda small at the All-Stars!