Depending on which characters your son would most enjoy there are multiple options!
Garden Grill (Epcot) is a good one where you will dine with Chip, Dale, Mickey, and Pluto. The best part about the character interaction, at least in my opinion, is that the characters come around to your table a lot. At many character dining meals, you will only see the characters once. Here, they keep walking around the restaurant and will visit your table 2, 3, or even 4 times. The food is also very fresh and is served family style so you don't have to worry about leaving hungry or missing a character while up at a buffet.
Ohana (Polynesian Resort) was a favorite breakfast for my family on this past trip. You will get a picture made before you are taken to your table. They have an assortment of sweet breakfast breads and a very good juice at your table, as well as a fruit plate. Then, you will get an assortment of bacon, sausage, eggs, and very good potatoes. We also received a healthy platter with vegetables, egg whites, chicken sausage, and turkey bacon. Like the Garden Grill, this is served family style. The characters are Lilo, Stitch, Mickey, and Pluto. They also have a character and kid parade that the kids really seem to like.
Crystal Palace (Magic Kingdom) is good. It has a breakfast lasagna that is to die for. This dining includes Pooh and friends. My advice is to book this reservation for before the park opens so that you and your family can get your picture made in front of the castle with no other guests in the photo.