No character breakfasts @ US or IOA. You can dine with the characters at the 3 on-site hotels (usually Woody Woodpecker, Scooby and Shaggy):
Sunset Grille @ HRH- Sat. night
Trattoria del Porto @ PBH - Friday night
Islands Dining @ RPR - Mon, Tues & Thurs
If you page down on this forum a few people have written about their experiences.