As has been mentioned Chef Mickey's is the best place to see all of the Fab 5 characters. The buffet is excellent with a lot of choices and tons of stuff for the little ones.
I prefer dinner to breakfast because they have an amazing dessert bar. While the breakfast food is good that dessert bar sits there empty mocking me in the morning.
I'm surprised to hear that Minnie isn't at the Tusker House. I know she has been there in the past, but they do change the rotations. The Tusker house has some nice exotic additions to the breakfast buffet, but you will still find the same All-American basics.
Mickey joins Stitch at 'Ohana's for breakfast. The highlights there are the raucous atmosphere, the island fresh menu, and it is all-you-can-eat table service rather than a buffet.
Cape May is great if you have a family that loves seafood, or you are staying at the Y&B.
Hollywood and Vine is only worth it if your kids are really into Handy Mandy and his friends.
1900 Park Fare offers the unique experience of having the characters talk. The food is excellent, especially for breakfast, and the conversations can be hilarious.
The princesses do talk at their two venues, I prefer EPCOT, due to the variety of princesses, but they honestly don't say much. Alice and the Mad Hatter may not be as refined, but they are much more interesting meal companions.
Finally, the Crystal Palace has the Pooh characters and a beautiful setting. Dinner is great, but breakfast is divine. An early seating gets you in the park before rope drop. It is amazing to walk down an empty Mainstreet USA and get a picture in front of the castle with no one else around. The food is outstanding. I literally wake-up dreaming about the puffed French toast as my vacations approach and you have to try Pooh's Breakfast Lasagna at least once. This is also a great spot to introduce very young guests to the character experience. The pooh characters tend to be physically smaller and less rambunctious than other characters. I start every vacation here.
If Mickey and Minnie together are your priority and your only doing one I'd do Chef Mickey's for dinner. If your flexible my recommendation is Crystal Palace for breakfast. All of the character meals will include a basic kids section to please even the pickiest eaters.
I know this is way more than you asked for, but I got going and I just couldn't stop.
One last note if you are into the buffets I suggest hitting them for breakfast and lunch. You will burn them off through the day and the lunch price can often be a few bucks cheaper. Going to bed right after any of these does not make for a pleasant night or following morning.