My kids would never dream of asking for a fiber-rich snack. I just don't tell them that the apples or endamame snack are fiber-rich.
Why is fiber so important? Besides helping maintain good digestive health, fiber-rich foods are more filling and discourage overeating.
Kid-friendly fiber includes fresh fruit such as apples, berries, oranges, and pears. Whole grain cereals, beans, and endamame (a crunchy soybean snack) are good choices too. My kids like the Fiber One cereals and muffin mixes.
For more info on adding fiber to your diet check out this link:
http://kidshealth.org/parent/nutrition_fit/nutrition/fiber.html