Combine macaroni, cheeses, salt and pepper in slow cooker. Pour milk over top. Cover; cook on LOW 2 to 3 hours, stirring after 20 to 30 minutes.
Stir in sliced hot dogs or desired vegetable.
As with all macaroni and cheese dishes, as it sits, the cheese sauce thickens and begins to dry out. If it dries out, stir in a little extra milk and heat through. Do not cook longer than 4 hours.
This is a simple way to make macaroni and cheese without taking the time to boil water and cook noodles. Kids can even make this one on their own.