Fruit juices contain much simple sugar without much fiber. Many people think of juices as health foods. This simply isn't true. In small quantities they are fine, but they are mainly a way to get many of the calories and some of the nutrients from a substance, without getting as full and without getting the needed fiber. And children who drink more than 12 ounces of fruit juice per day are shorter and fatter than those who don't.
Fruits contain lots of sugar, but it's in a form that's intended for the body to use.
Instead of sugar-coated breakfast cereal, try cereal with berries. Most kids like this. They enjoy the treat, and it stays healthy. Children do not need large amounts of refined white flour. Again, in this century, white flour has become a major part of our diets.