May I also pipe in? I have a suggestion. Part of the fun of being at WDW is absorbing some of the atmosphere. Which is why some of the restaurants are very popular. Don't deny yourself or your kids the fun of the experience. Given the ages of your children, and that it's your first visit, I'd definitely suggest trying to make reservations for the following:
50's Prime Time cafe (think "I love Lucy's kitchen; waitstaff are the entertainment)
Sci Fi Diner (clips of old scifi movies are shown and it looks like a drive in)
Chef Mickey's (buffet with Mickey and friends, or the " Fab 5" as they're called)
Liberty Tree Tavern (character meal with Colonial-style Minnie Mouse, Goofy, etc)
Crystal Palace - has Pooh and friends
If your children are into the princesses, the
Askerhaus Restaurant in the Norway Pavilion at Epcot would be the place to eat Most of the princesses are there, and the little girls do dress up in their best princess outfit.
I would also suggest,
Chefs de France at Epcot for
lunch so that your children will get to meet "Remy" from the movie "Ratatouille" who appears at your table.
Going to WDW in the middle of July will be VERY HOT AND HUMID AND CROWDED. Please, please, please, make at least one reservation for one sit-down meal a day for whatever of the four parks you'll plan to go to. Your feet will thank you, and you'll feel so much better out of the heat. It can get sooo frustrating to be hungry and turned away from a restaurant because it's full. If you don't want to eat at the time of the reservation, you can always cancel, as other posters have said.
Oh, and by the way, (and this has nothing to do with dining reservations, but we are obsessed with making sure you have a good first trip!!!) make sure your family drinks a lot of water, uses sunscreen, wear comfy, broken-in shoes, and your kids have sunhats. Florida sun is brutal. Have a wonderful trip, oh, and "Welcome! to the DIS"