First, realize that there is no way you can do it all in one trip!
Cinderella's is purely atmosphere. The food isn't that great, and it costs 2 TS. That said, with a 4 year old DD, it is probably a "must do." Make your reservations way in advance. You might consider the princess lunch in Epcot as an alternative if you can't get reservations for the castle.
Cap'n Jack's is a walk in and wait restaurant--they don't take ADRs. This might not be good with a 4 year old.
Your best "bargain" on the
DDP is character dinners rather than breakfasts. There are good dinners at 1900 Park Fare (Cinderella, fairy godmother, sewing mice), Liberty Tree Tavern (Goofy, Minnie, Pluto, Chip & Dale), Garden Grill at the Land in Epcot (same characters), Chef Mickey's (same with some additions", Crystal Palace (Pooh characters.)
Personally, I didn't like Donald's breakfast at AK. . Food was just ok, characters were rushed. Breakfast at Cape May Cafe at Beach Club is good, and easy to do on an MGM or Epcot day.
Coral Reef is great, and the fish will keep DD entertained. COncourse Steak House is good.
You can see the menus (all are subject to change) at allearsnet.com Decide what kind of food you like, and make your ADRs appropriately. Remember that with a 4 year old, you don't want to eat too late.