For us, our "must-do's" are the following:
Breakfast at Chef Mickey's
Breakfast or Lunch at Cinderella's Royal Table
Lunch at Crystal Palace
Dinner at Liberty Tree Tavern
This year, we're also trying Donald's Breakfastasauras at the AK & Garden Grill at Epcot.
1900 Park Fare looks wonderful, and, some day, I'll be able to fit it into our plans! (I thought about scheduling breakfast at 1900 Park Fare instead of at Chef Mickey's, but then decided we couldn't give up Chef Mickey's.) But, I'm wondering if your son would like dinner there - it seems a little "girly" if that's the only character meal you're doing.
Liberty Tree Tavern is great - but Mickey's not there - just Minnie, Goofy, Pluto, Chip, & Dale. Food is yummy - served family-style.
At the Garden Grill at Epcot, the food is also served family-style. The characers are Mickey & Chip & Dale, and the restaurant slowly revolves as you're dining.
I love meals at the castle - at dinner, it's the Fairy Godmother & the mice (Suzy & Perla) - they don't circulate among the tables, but they have a special "wishing presentation" thing they do in the dining room. Cinderella is in the lobby for pics.
Breakfast at Cape May Cafe looks cute.
Donald's Breakfastasauras looks like another fun one - we're trying it this year for the first time. The servers sometimes even get into the characters' antics.