Buffets are a great use of the dining plan! At around $35-$40/adult, most only require 1 credit.
For a Magic Kingdom day, I'd recommend Chef Mickey's (Mickey & Co. dressed in chef's gear @ Contemporary Resort) or 1900 Park Fare (Cinderella, Prince Charming @ Grand Floridian Resort) Unfortunately, Cinderella's Royal Table would require 2 credits on the dining plan.
EPCOT: Akershus Royal Banquet Hall (Norway) has many princesses like Belle, Ariel, Snow White, Cinderella, etc. And a complimentary picture too!
Garden Grill is a unique, very slowly rotating restaurant with Mickey & Co. wearing farmer gear. It's a set menu that you can get as much of as you want. Not a 'typical' buffet.
Hollywood Studios: There's a Disney Junior character buffet at Hollywood & Vine for breakfast if your daughters are fans of Princess Sofia.
Animal Kingdom: Tusker House for lunch (Donald, Daisy, and Goofy in safari gear). Great atmosphere and more unique food.