OK. I have done Disney on various budgets...We've been before with DH's bball teams, I made a big batch of chex mix from scratch and added m&m's and nuts and other faves and then divide up into several gallon size bags for each day to keep in our backpack. We always carry water bottles and refill. I bring fruit snacks, etc for the backpack. Almost always eat bfast in the room, except for cindy and storybook bfasts

We also like to eat 1 bfast inside MK at the bakery? can't believe the name escapes me...We have found that taking a break in the middle of the day and eating at a chain 'saves us money'. I find it hilarious that when we go to Olive Garden for lunch (lupper) it helps our budget!!! There is also a CICI's Pizza that would be great for your budget with the growing kiddies. We make sure the kids get big salads before the pizza and dessert

These are good ways for the one meal a day to stay in budget.
OK for the DDP. Hope nobody screams at me for this...but I am very frugal. If you are staying for more than 4 nights, you might consider splitting your stay. Say the day you arrive you book 2 nights, with tix, and DDP. You can use those 2 TS, 2 CS, and 2 snacks over 3 days. If you are already doing TS for sure, this may save a little. If you and DD go to 2 princess bfasts, then you will use yours up with this, then have CS and snacks for 3 days. If you use the credits for the boy's TS meals where you can get more value...Each TS credit gets an appetizer, entree, dessert, and drink. 2 TS definetly enough to feed 4, maybe 5. I know I (and my kids) sometimes order app as entree...
Splitting the stay...if you want to change resorts, or even if you want to stay in the same place, they will move your bags for you (I'd tip) while you are in the parks

Then, with your 2nd ressie, do room only, use your same tix and don't add DDP.
I am staying in a DVC villa (a good friend is a member) for the first time this spring with a full kitchen..can't wait to see how I stretch my dollars on food. We can't justify the DDP for our trip. Oldest DD just turned 10. I can't justify DDP or even a character meal as little as she eats.
Enjoy your stay and whatever you do, at least look at the menus to know what your up against.
We also get a good value at Pecos Bills, Mexican counter service at Epcot.