I asked a question about this not too long ago. I wanted to buy Mickey waffles to take back to our resort rooms for breakfast. I asked if I could buy a kids meal, because I want my waffles shaped like Mickey, even if I am 32!
The consensus on that thread seemed to be "Go for it!"
The reason I was concerned enough to ask, though, was that I seem to remember the menu boards saying "Kid's Picks (Children 9 and Under)".
While it doesn't seem like a big deal to me for an adult to order a child's menu, if the posted "rule" says 9 and under, I could see why some would see this as an issue - after all, don't we debate the posted rules about mugs, line jumpers, pools, and etc. endlessly around here?