Not all cereal is bad, but experts say this one is the worst. High in sugar and sodium, it offers little nutritional value.

Dry breakfast cereal has always been marketing-driven. In the 1930s, Mickey Mouse was recruited to endorse Post products; Cap’n Crunch was created to appeal to kids who hated soggy cereal.

And this category of kids' cereals is a lot trickier than its fruity counterpart. Many well-known brands have churned out chocolate versions of their cereals over the years—everything from Chocolate ...