Take a look at the list of ingredients in Cocoa Puffs: corn, sugar, corn syrup--all high glycemic index foods.
In other words, Cocoa Puffs is the physiologic equivalent of pure table sugar. Sure, it comes packaged with this wacky bird and the back of the box usually has fun games and offers. There's also the clever, fast-paced TV commercials to remind you of how fun Cocoa Puffs can be.
What is the actual consequence of a breakfast of a food like Cocoa Puffs in a cup of skim milk? That's easy: A big surge in insulin and blood sugar (from the corn and sugar), a drop in HDL cholesterol, surge in triglycerides (from the sugar and sugar-equivalents), increase in small LDL. Beyond this, you raise blood pressure and experience an insatiable increase in appetite. Then you get fat. 
Obviously, none of this is desirable. Then why does the American Heart Association allow its Heart CheckMark endorsement on the package?
The Heart Association is trapped in 1982. Low-fat was in, saturated fat was the sole enemy of heart disease.
In 1982, the evils of small LDL, for instance, were unappreciated. LDL cholesterol was LDL cholesterol--all of it was bad and saturated fats seem to raise LDL. But the story has evolved enormously since then: LDL is not all the same. Small LDL is among the principal culprits in heart disease, the same small LDL hugely magnified by Cocoa Puffs and other similar products that fill 70% of supermarket shelves.
The American Heart Association needs to get with the times. The conversation on healthy diets has progressed considerably. Yet garbage foods that wreak havoc on health like Cocoa Puffs continue to be endorsed by an organization that still carries substantial clout with the American consumer.
My advice: Until they change their tune, anything that carries the endorsement of the American Heart Association should be eliminated from your diet.