We went this past May for a first time family visit with a 9 year old boy and a 6 year old boy. We did Chef Mickey's for a later breakfast, and they liked that since it had all the biggest characters - Mickey, Minnie, Donald and Goofy. My youngest really didn't want to see the Disney Jr characters at H&V, plus the food is only so-so, so we didn't do that one.
As we were walking through the park, they saw Crystal Palace lit up one night and asked to go there, so we are going there this November for dinner. One poster suggested Ohana, and that only has Lilo & Stitch as characters for breakfast - your 6 year olds might like them. For dinner, it is a Hawaiian type of entertainment, but both boys thoroughly enjoyed the conga line and playing limbo and the flower leis, and liked the foods as well. I've also been told that 1900 Park Fare dinner, which has Cinderella,the Prince, the Stepmother and the Stepsisters, is very enjoyable, even for boys and parents. Apparently, they really play up their characters and are a riot. The food is pretty good. So we have that scheduled as well.
Keep in mind that the 6 year olds tire out. What we found worked best for us, was to let them sleep in, eat a light breakfast in our room, and hit the parks a bit later, so that we could close them down, when many people have left. We were always in the parks around 10-10:30. And it worked like a charm. We did take a breather in the afternoons a couple times for the late night hour parks by heading back to the hotel for a swim and some rest. We lasted until midnight and later with no crying like others had around us.
And if you are interested in a breakfast that isn't one of Disney's, the Hilton across from Downtown Disney has a Sunday morning character breakfast with Minnie, Pluto and another character (Briar Fox was there for our visit). The food is good and the price is very low. Its a good way to get more characters without laying out a fortune.