Is the breakfast conversation an example of direct or indirect characterization?

Your question could be answered in more than one way. I see both indirect and direct characterization in the breakfast conversation.
There are many obvious instances of indirect characterization in this scene. The author continually uses Mary's speech and thoughts to present her as forceful but warmhearted; judgmental yet sympathetic. By having Rudolph say Mrs. Marshall shouldn't have been lifting heavy milk cans, the author is characterizing him as cautious and caring. She is also using Mrs. Marshall's actions and another character's reactions to suggest that this character works hard but may push herself too much. Indicating that the boys' heads are "close-clipped" and that Mary "flushed so red" at the doctor's compliment, the author uses these characters' looks to show that the boys are carefully groomed and that their mother is modest despite her outspokenness.
There are also a few examples of direct characterization in the breakfast scene. The author interweaves direct and indirect characterization when she writes that Rosicky turns toward the doctor "with the instinct of politeness which seldom failed him." And she states directly that when Mary likes people she feels "physical pleasure in the sight of them, personal exultation in any good fortune that [comes] to them."
For more information about direct versus indirect characterization or more insight into characterization in "Neighbor Rosicky," you may want to check out the links below.
http://www.literarydevices.com/characterization/

http://www.readwritethink.org/files/resources/lesson_images/lesson800/Characterization.pdf