Disney standard characters. This is Mickey, Minnie, Donald, Goofy, and a host of Princesses. There is a wake up with Disney Jr. program, but I am unsure what characters come to that. There is a character breakfast trial that seems to pop up periodically. It is younger characters, but may only be offered on the Fantasy presently. On Pirate night Jack Sparrow, Captn Hook, and Smee often appear.
Captain America is on the Magic as part of the Marvel upgrade. Depending on when your sail date is, there will be a Jedi training activity added to the kids club on the Dream.
Gravity falls will have a hard time filling those characters as those are live action children. You don't have that problem with Sofia or Jake the Pirate because those are cartoony and easily adaptable. But I have not heard of those characters ANYWHERE.