In Western culture, especially heavily Christian ones, Sunday for a grand majority of people is known as the day of family since usually that's when said christian families go to church together, have sunday lunch/dinner and generally spend the day with each other. It is common courtesy for people with children, primarily crying and screaming babies, to NOT go to an opening weekend or at least wait for Sunday. Little talkative children are fine for films aimed at them or even popular with their age group and somewhat close in rating [aka a PG-13 superhero film]. So I got the notion from living in a western culture.