Eat a big breakfast and bring snacks and water to the park.
If you want to do a character meal and not spend the $ try the Ice Cream Social at Epcot's the Garden Grill Restaurant $6.99 a person adults and children good price!!! and you get ice cream, yummmy!!!!
Meals eat out of the park, obviously I would recommend Sweet Tomatoes, its buffet and really yummy!
Have relatives give the kids disney dollars for birthdays or holidays (including easter instead of to much candy) Have one specific day to go to Downtown Disney and let them spend the money on what they want. Let them know this before going in the parks so they know they will have a day to spend. If you don't want to ask relatives, give them specific chores to do to earn some money for Disney and put it in a clear piggy bank for each of them that they are not allowed to touch they will be able to track thier progress and it might get them to do more to get more. Let them roll the change and change them for disney dollars just before you leave.
Hit the sales at the
Disney Store or Disney Direct this past weekend I just got sweatshirts for everyone for 9.99 a piece, bring your treasures to the parks and leave them for the kids in the morning from Mickey as a little treat could be anything from a lollipop to a glow necklace (night parades) to a t-shirt. You wouldn't believe how much $ you can save.
They have a campfire program at Fort Wilderness that is free (features chip and dale) and then a Disney movie plays (also free). Then you could go down to the FW beach and watch the Electrical light pagent and you can see wishes right after the pagent (also free). (I am not totally sure all these are just for resort guest, you might want to check on that). If you wanted to make it a whole night, FW Trails End puts on a great buffet for good price, that would give you reason to be there, then enjoy the rest of the events.
That is all I can think of for now!!!