> That's why any kid can go watch any movie in the cinema right?

Yes. At least in the U.S., the federal government does not regulate that, it is voluntary by the MPA (formerly MPAA) and theaters. A kid can buy a ticket for a PG movie and walk into an R-rated movie.

> Do you think a middle class single mother has the resources to keep their kids entertained and out of social media for the whole day?

Mine did. While not everyone has a backyard, things like pencils, papers, books, used toys, etc can be found inexpensively or for free.

So why are there laws that dont let them buy cigarettes and alcohol?

Did social media exist when you grew up?