M.B.
Things that really get my son going are pears, sweet potatoes, peas, corn. We also use whole grain bread only never white and Ronzoni pasta even if you use the white version of it it has a lot of fiber. Any fruits and vegetables and grains will help. Also beans are super good fiber. Let me know if you need serving ideas and such. There is a great recipe using peas that makes little pancakes that helps getting them into a picky eaters diet.