"Little Johnnyism" is a variant of fallacious appeal to authority. Parents used some variant of "Little Johnny" to convince us of how to behave: "Your cousin does the dishes", "Little Amanda keeps her room clean", "Little Johnny mows his parents’ lawn", and "The starving children in India would love your mother's cooking". Our parents assumed that such comparison to Little Paragons of Virtue would convince us to behave as our parents wished.
Religionists, in arguments that are not elevated above such childish fallacies, assume that examples of prominent believers–authors, scientists, etc–demonstrate that we all ought to be believers. Logically, all that these "Little Believer" examples demonstrate is that those who were indoctrinated as children may retain ridiculous credulities despite later achievements.
Little Kirkism appears to have been coined by Arthur Vandelay: "
Some apologists, like Kirk Cameron, will even cite (or, as I suspect, manufacture) their own atheist pre-history and subsequent conversion tale—call it “Little Kirkism”—and then claim to know what all atheists think (and presume to tell atheists what atheists think)."
As a group, united only by disbelief in Yagoal* or Brahman, atheists certainly do not think alike, though most whose disbelief arises through a logical refusal to believe ridiculous mythologies will be, by extension, immune to these "Little Dimmism" fallacies of logic.
* This term is derived from a concatenation of the "Yahweh-God-Allah" Abrahamic deity.