Final answer:
Parents reminding their children not to chew with their mouths open is a matter of social etiquette and falls under the topic of social studies.
Step-by-step explanation:
When parents remind their children that they should not chew with their mouths open, they are engaging in the promotion of good table manners. This falls under the topic of social etiquette, which is a part of social studies. Social studies deals with the study of human society, including aspects such as culture, behavior, and relationships. In this case, parents are teaching their children about appropriate behavior and manners during mealtime.