Parents need to know that this game features Wario, a crude antihero to the squeaky-clean Mario. Wario enjoys picking his nose and smacking his butt, among other things. There's nothing overtly offensive about him, however, and the character is actually quite funny and endearing in spite of his greed, which is his primary motivation for helping the subjects of the Shake Dimension. Aside from boss battles, there is scant combat in the game. Wario can stomp on enemies, shake them, pick them up, and throw them into walls or at each other, but this is often done in the context of solving a puzzle.
My 5 yr. old really enjoys this game, however, he does need some help to get through some of the earliest sections. The game does do a great job at incorporating the Wii remote motions into specific moves for Wario which add to the fun.