Andrew-
My boys have had nothing but glowing things to say about the OC. If you ask them about their cruising experiences, they will tell you how awful, how small, and how little there was to do on Royal Caribbean and Carnival (in their kid areas). And then they would tell you how much fun they had, and how many friends they made on Disney. As a matter of fact, there were times we had to pull them out (they were that intent on staying). Which led to the rule that required family time is breakfast and dinner. Everyone must attend.
But that does not answer your wife's questions about safety. Unfortunately, when it comes to stories about Disney (or any place else for that matter) it is always the sad, scary, or disturbing stories that get attention. While the stories about the wonderful experiences are missed or not even noted. (side note...Tink moment... I have worked very hard as of late to make sure to leave positive reviews when something good happens, not just negative review for the bad. It is sad but true, that we can find time in our busy lives to talk about how bad something is, but rarely find time to share about the outstanding things). I have not heard the story about the child falling asleep in a stack of chairs, but find it odd that my husband and I were talking about children falling asleep (or there inability to fall asleep) in the OC just last night. Someone had asked us "if my child falls asleep in the kids area, do I have to bring them back to the room, or can we just leave them until they wake up?" First I have to explain how floored I was at the question, but answered quite nicely that I honestly would not think that falling asleep in the kids are was possible. There is so much going on in there, that falling asleep would be difficult. And if a child was found sleeping in a pile of chairs, I am sure it was because they were so tired, and that they wanted to sleep, so the found someplace with no activity going on. The good news is, all the children are given RFID bands when they are signed up for the kids program. These bands are scanned when they go into the OC, and again when they leave. If a child is proving difficult to find, a cast member can pull up the child on the computer and see whether or not someone has signed them out (and don't worry, you have the chance during sign up to designate who can and can't sign your child in and out). {Another side note, with the RFID band, your child should be able to be located no matter where they are on the boat.} Basically, if you or your wife are the only ones allowed to sign them in and out, than if neither of you signed the kiddos out, they would still be there. There are occasions when one of the activities is scheduled for out of the OC (like a game up on the sports deck). On these occasions, they are with OC cast members who keep a good eye on them. They will document who they take with them, and make sure that is who they have with them until they return (and if you come to the OC during that time, they can tell you where your kiddos are). Oh, and I don't know if it helps or not, but the OC on the Wonder is smaller than the one on the Fantasy or the Dream (the larger ships have several rooms, and hallways connecting them). And the story probably came from one of those ships. To put your worries at ease, they will have an open house on our first day aboard, and you will get a chance to see how secure the OC is, and how many cast members they have on hand to watch over the kiddos.
Now, Cabanas at Castaway...I wish I could put your mind at ease as hopefully I did about the OC, but I can't. I can verify that all of the Cabanas are taken. We are gold members, and they were all gone when I logged on at 12:01 AM on the day that online check in opened for Gold members. We had wanted to get one for a large group of us that are going. What you can do is go straight to the guest service desk when you get on board and ask to be put on the waiting list for cabanas, and then keep your fingers crossed.
If you do not get a cabana, don't fret, there are a lot of great areas on the island. My family has a tradition of hitting the game area before lunch, and then we find a nice place on the beach that still has undisturbed beach chairs and umbrellas, and make ourselves comfy.
On sea days, the Mickey pool and family pool is a hit or miss kind of thing. If there is a family activity going on around the pool, or a good movie on the mega tron, they will probably be on the crowded side. However, earlier in the day and late afternoon, it is thinned out. Other than that, it is hard to say until we get on board and see if we are on a sold out cruise or not. Either way, I think that you should be able to find a beach lounger to put your stuff on, and room in the pool. The hot tub on the other hand is always packed. If you want to use a hot tub, I would plan to do that when you can go to the adult only area.
Hope that helps,
~Tink~