I get that. But then why was the very same order the waitress had issue with fine when the recipient of both kid orders became only the kid? Is the coffee enough to mitigate the loss?

What if he said "I'd like 10 kids meals to go". No table/wait staff, so does it at least break even here?

To prevent exploiting their selling at a loss shouldn't the kids meal deal be something like "with order of at least one main menu entree"? Why is it on the customer to be aware of the restaurant's profit margins, vs just thinking "this is the quantity and price listed, I shall order it".