The political cartoon referred to was by Jeff Parker, has been an editorial cartoonist for Florida Today since 1992. The overall message being conveyed by the referenced political cartoon is that advertising on school buses could have a negative affect on children.
Certain states in the U.S (e.g. New Jersey, Texas, Massachusetts among others) permit school districts to sell ad space on school buses in order to raise funds for school activities. Some have argued that these ads unfairly target young, impressionable consumers, and as such should be stopped.