Last year I posted this mock-up packaging design for a new General Mills cereal in the Sea Creatures Rule! thread. Today I remembered about it and decided to do some digging and see if this cereal was actually going to happen, and I did find something, although it's a different cereal to the one proposed in that mock-up.
The only website I can find that actually shows it so far is a nutritional website called ShopWell.
Presenting: SpongeBob SquarePants Fruity Splash.
The only other mention of this cereal I can find so far are some recipe pages on Pillsbury and Betty Crocker (brands owned by General Mills) that use the cereal in recipes, but if you click on them you get taken to a 404. I did manage to find this picture of the "Fruity Splash Smoothies" recipe, though, which clearly shows SpongeBob and Patrick cereal pieces.
Since the images and the phrase "SpongeBob SquarePants Fruity Splash" only start appearing in Google searches from April onward I'm going to guess that the cereal isn't actually out yet but is due to come out very soon.
So keep an eye out and let me know, I guess. Not living in America, I can't just walk into stores and start looking for this stuff.