Kids can be such picky eaters. . .here are some things that worked for me. I use my food processor and shred up zucchini, carrots, broccoli, and cauliflower and such into normal food my little one will eat, like spaghetti sauce, mac and cheese, grilled cheese sandwhich. You can disguise cauliflower in a lot of things if you cut it up small enough, broccoli too.
Also switching to whole grain pastas, breads, waffles, pancakes and cereals will help provide fiber like some of the other moms stated. One thing my son liked was zucchini and banana bread that I made myself. Also some kids are more intertested in fun foods, like ants on a log (a celery stick with peanut butter and raisins as the "ants"). Our son got in some fruits when he would go on his hunger strikes by us mixing them in his favorites, like pancakes with fruit in them, yogart, applesauce now comes in different flavors and individual packs at the store. My son liked the mango applesause.
Pear juice of any kind will make a child have a BM.
I am a nurse, and I would get a second opinion if my doctor had suggested the mineral oil after a two year refusal of fruits and veggies if he fully understood the length and details of the eating problem. Second opinions can never hurt, but bad medical care can.
also here are some web links for picky eaters:
www.askdrsears.com/html/3/T030800.asp
www.keepkidshealthy.com/parenting_tips/picky_eaters.html
parenting.ivillage.com/tp/tpnutrition/topics/0,,4rvl,00.html
www.babycenter.com/refcap/toddler/toddlerfeeding/9199.html