[Article update at bottom] During yesterday’s English localization of the Terry Bogard livestream for Super Smash Bros. Ultimate, one quote from Masahiro Sakurai jumped out at viewers and took off on social media. That video had Sakurai say that Mai Shiranui was excluded from the game because “Super Smash Bros. Ultimate is for good boys and girls of many different ages, so we decided not to feature her.” However, GameXplain has revealed that Sakurai did not say such a thing in Japanese. Instead, he just talked about the game’s age rating.

In Japanese, Sakurai apparently said Mai wasn’t included in Super Smash Bros. Ultimate in order to keep the game’s CERO A rating in Japan, which is the equivalent of an ESRB E rating in North America. According to the video, a woman who can be perceived as sexual from basically any angle in a video game could affect the game’s Japanese rating, which would understandably make Mai a hard sell.

The “little boys and girls” quote was added by Nintendo’s localization team, seemingly for flavor and entertainment value. Mission complete on that front, but fans may also be disappointed to learn that the funniest part of Masahiro Sakurai’s presentation wasn’t something the man actually said.

Update: Trusted translator PushDustIn is offering a contrary explanation, saying Sakurai does literally say “good children” and that we should be mindful that there are not always 1:1 translations for things.

???????????????????????????????…? ??? literally means "good children". They just translated it as "good boys and girls". There are often more than 1 way to translate things. — PushDustIn (@PushDustIn) November 7, 2019

So Nintendo localization may have still added some embellishment and removed mention of CERO, presumably since that has no effect on North America, but it now seems the localization did preserve the essence of what Sakurai said.

[Source]