According to ESRB, this game contains: Comic Mischief
Parents will probably find little here to concern them, as the game manages to entirely stick to topics appropriate for children. If your children are old enough to watch cartoons, then there should be no problems with WarioWare.
Gamers with gamer friends and a GBA will truly want to check out WarioWare. It's great fun, not only in terms of the multiplayer games, but just passing around the GBA and hearing your friends make amusing sound effects as they try and deal with whatever WarioWare might be throwing at them.
Deaf and Hard of Hearing gamers can buy this game with little worries, as there no audio cues within the game, at least as far as I could find (there are a lot of games).