My DD is 4 and although she has been potty trained for over a year and a half she still occassionally wets the bed. She is also big for her age (45 inches tall!) so maybe the whole brain thing is true! In the beginning, I used goodnights and they leaked for me also. Rather than change all the bedding at night, I bought about 3-4 of those absorbent crib pads that babies r us sells. They are a felt like material on one side and vinyl on the other. They work great! I layer them so that when she does wet the bed, I just take the top 2 off and I still have another 2 to protect the bed while I wash the other 2. She has gotten better over the last 6 months (she is currently 4 and 4 months old) so I have her sleep in underwear only now..But the pads keep me from having to clean the mattress if she does slip up.
I had no idea that WDW provides a rubber sheet for these problems. I was going to bring my pads down there with me in Feb. But now I'm glad that I can leave them at home! Thanks Dis boards, once again, for helpful info!