I think there's also something to be said here about the fact that a child of age 7 was allowed to play a game rated age 13+. Sure, "its cartoonishness allayed their worries"....but the decision to rate a game for a certain age is taking in a lot of different factors. If you take a 7 year old to a PG-13 movie which then traumatizes your child, you don't get to complain that "the poster looked so cartoony so I thought it would be fine" and then claim that it's the movies fault.

That said, I do believe that online games ratings should take into account additional factors like monetization models, expected screen time, tendency to be habit-forming, and that information presented to the parents. Really I feel that parents are underequipped these days to deal with the volume and types of media their kids have the ability to consume.