Can a 12 year old watch Ouran Highschool Host Club?

Ouran High School Host Club can almost be seen as a shojo version of a "harem" manga, except that it's one girl surrounded by several boys. ... I would definitely recommend Ouran High School Host Club to female manga readers who are 13 or 14 years of age and older.

Is Haikyuu ok for 13 year olds?

While there is one girl in particular some boys fawn over, it's not perverted or inappropriate. Making Haikyuu one of the most legit animes to watch with family or kids. The simple, easy to follow story makes this show even more appealing as well. And might end up being one of the top shows you've watched.