I was a teeny bit concerned that our almost-2-year-old wouldn't be on the DDP with us, but when I thought about it further, she normally shares whatever we get anyway and it wasn't a big deal. At table service restaurants, we chose buffets & family style as much as we could... we did Crystal Palace for dinner and she had her own plate and milk and we weren't charged for either... we did Tusker House for breakfast and the same thing, no charge... we did the Prime Time Cafe and she just shared off our plates (our server brought an empty plate for her to use) and got a milk, and there was no charge and PLENTY of food for all of us... we did the Norway Princess Storybook dinner and expected her to share our meals, but the server actually asked us to choose a kid's meal for her complimentary, so she got that and a milk (and a plate from the cold buffet) all for no charge. There was always plenty of food for TS restaurants (don't forget that you get a dessert, too, which on top of an already-too-huge entree will make sure that everyone is quite full!).
For CS restaurants, the portions are also pretty big so DD always shared with us there, too. If the meal was a teeny bit smaller than others and we were a little hungry later, don't forget that you have all those snack credits! We used a few to share when our reservations or timing were just off, and the rest we had to use up the last day at Goofy's Candy Co because we just were never hungry enough for a snack (after all the food at CS and TS restaurants). The reality is that Disney portions are WAY bigger than most places (or at least bigger than they should be!), so unless you're all extra hungry eaters, you'll have plenty of food amongst you all (and our trip had me, a very-hungry pregnant lady and DH who's 6'5 and has a metabolism like crazy and eats a lot).
OH, and also, don't forget that at some CS restaurants you can get a bowl of fruit as your dessert, so we did that twice for our DD (she's happier with a bowl of fruit for lunch than many entree items and it ensured that she got a little more healthy food), and you can also always get a cup of ice water for free which was great because of we got a soda, she could have the water (she hates soda, and I'm fine with that!

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