I don't know that there's a character dinner, but I did take my boys to a character breakfast in Islands of Adventure. I think the restaurant is called Confisco Grill. It was fabulous! The big star was Spiderman. He was so much fun. He gave my son a "secret signal" in case he needed his help during the day. He spent a lot of time at each table & really made it fun for the kids. He made my little one's whole trip. He was five at the time.
There was also Cat in the Hat & Thing one & Thing two. The two Things were a lot of fun too. They did mischievous stuff like turning the salt shakers upside down & pretended to steal food from my kid's plates.
The food was pretty good for a buffet. Nothing super fancy, but we left satisfied. I would definetly recommend it!