Last year my 3yo was quite concerned about the characters not talking. I tried to wave it off and just say "they can't" but he was too smart for that. "Buzz talks in the movie, why can't he talk to me? Mickey talks on our MK DVD, why can't he talk now?"
Well, I know this will sound like I'm a party pooper...but back then my kids knew Buzz was voiced by Tim Allen...They see the snippets of the new cartoons being made (usually on the disney channel) and recognize many of the human personalities, they understand cartoon characters are not real.. yet their faces light up and they giggle whenever they see them. (They also understand the person in the Buzz costume is a stranger). But, that being said...they never came out and asked me about them. One time my 5yo son said.."I hope they let that person get out of that costume..It's hot out here!" so I just said "It sure is."
We had a funny incident where Cinderella-in toon town-made a unique comment/greeting to my son (8yo). Then the next day "Snow White" -at the castle-made the exact same comment/greeting. He laughed the whole way back to our table and whispered to me that it was the same person, as if I hadn't caught on..LOL.
Good luck coming up with something!