How do we know? Well, Kotaku has learned that the Entertainment Software Review Board (you know the ESRB-- those people who are fairly ineffectual at keeping adult games out of the hands of children?) has rated the game (E for everyone, yay!). Here's the full description:
FINAL FANTASY IV: The After Years
Content descriptors: Alcohol Reference, Mild Fantasy Violence
Rating summary: This is a 2D role-playing game in which players embark on an adventure involving magical crystals and a mysterious kingdom. Players traverse across a field map or through dungeons and can enter into turn-based battles along the way. Players use a menu screen to select attacks or magic spells against tiny enemies (e.g., leopards, birds, knights, fish monsters, etc.) that blink and disappear when defeated. An item called "Bacchus Wine" is occasionally used to defeat enemies in battle.
No clue when this will come out, but I for one am now looking into budgeting for a Wii.