That depends on your cereal choice. The Environmental Working Group (EWG) recently studied more than 1,500 cereals and found that a child would consume more than 10 pounds of sugar per year if he ate a typical bowl of cereal each day.
Ten pounds per year just from cereal alone! In this study, 181 of these cereals were specifically marketed to children, and every one of those had added sugars. Cereal makers claim this study ignores the benefits provided by a cereal breakfast, including added nutrients and fat free milk, and may, in fact, be more nutritious than other choices a child could make.
The bottom line: make smart choices when choosing a cereal for your child. The EWG says to avoid the ones specifically marketed to children, and instead look for cereal containing six grams of sugar or less.