These are some resources to make short cartoons in the classroom:
There are a good number of ways of publishing students' comics. These are three ideas.
Publishing students' drawings through Calameo. This is an example.
Make Beliefs Comix! is an easy-to-use online tool. The comics cannot be stored on line; once a strip is finished, it must be printed out (on paper, as a pdf document, or as a picture by using a screenshot).
It also offers a set of blank strips that can be printed out so the students create their own dialogues.
Pixton offers different types of licences (for schools, for professionals...) that require payment. Anyway, there is a free option, Pixton for Fun, that can be useful for creating short stories.