None of the character meals really involve any characters that are really rare, but 1900 Park Fare and Hollywood and Vine offer a few more semi-uncommon characters.
1900 PF breakfast...Mary Poppins (white dress), Alice, Mad Hatter, Pooh & Tigger are usually there
1900 PF dinner...Drizella, Anastasia, Lady Tremaine, Prince Charming, and Cinderella are typically the chars.
Hollywood & Vine...Oso, Handy Manny, Jake, and June...although, outside of Jake, this might not appeal to a 5 yr old.
And while not a character meal, Remy is on hand at certain points at les Chefs de France and if you can get in, Beast is at BOG during dinner service.
Dessert Party is offered in December. It should open up for ADRs at some point in early October. There's no set date or time though when it happens.