Do you know if they are going to be going to any character meals? That can make a little difference. General ones I see every trip around the parks are...
Mickey, Minnie, Goofy, Pluto, Chip & Dale, Cruella, Mad Hatter, Donald, Mary Poppin & Bert, Alice in Wonderland, Peter Pan, Gepetto, Pooh, Tigger, Buzz Lightyear, Rapunzel & Flynn (Fantasyland Meet & Greet), and they arnt as common but I have seen multiple times the Queen of Hearts and the Tweedles in Fantasyland, & Sully from Monsters Inc, Woody, & Goofy's Son Max in the Hollywood backlot. Dont forget there is also Pixie Hollow in
Disneyland where they can meet Tinkerbell. There are always 2 other fairies, Terrance seems to be popular as is Fawn. But you may luck out and see the other fairies.
In Adventureland you can do a meet and greet before Storytellers with Aladdin & Jasmine, and in Fantasyland there is a Princess Fantasyfare where children can meet the princesses. They very each show, but expect the popular Cinderella, Snow White, Sleeping Beauty, Ariel, Mulan etc. Princesses also be seen at Ariels Grotto if a character meal is lined up. Oh and before I forget to mention, I do believe on the pirate island they can find Jack Sparrow.