With a 5 yr old, banking on the fact that you're going full out from rope drop to about noon or 1pm, and you make your kid walk, they will probably sleep for a few hours in the afternoon. I don't believe subbing a character meal in would be a good idea. If your kid gets tired and cranky, the last place you want to be is in a character meal where, instead of having fun, they're miserable. Not to mention, you don't want to see your kid do a face plant into their food. I'd also look at what you're doing later that evening. If it's something that you want your kid to see, then I'd make sure they got the proper rest (nap) so that they're awake for it. If it's something that you can catch later in the trip or isn't as important and they fall asleep in the stroller or whatever you have, then hit the pool. At least with the pool you're at your resort and close to a bed should they get "tired" cranky.
Besides, with the Florida weather, it's always a decent idea to have it in the back of your head that the "everyday afternoon storm" is going to pop up, which, if your kid is asleep and you're just hanging out at the room, you aren't missing anything anyway.