According to ESRB, this game contains: Crude Humor, Mild Cartoon Violence
Parents don't have anything to worry about. The only violence in the game consists of Mario or Luigi jumping on the head of a cartoonish mushroom, smiley-face cactus, or non-threatening ghost. There is no blood, no gore, no questionable language, and certainly no sexual situations. If, as a parent, the Mario games can't be seen as benign and harmless, then your kids probably don't play video games at all. It might be a little tough for younger ones, but it's absolutely safe and harmless fun.
RPG fans will find a simple adventure that requires a lot of hand-eye coordination. It's fun and a great time-killer portable experience delivering approximately 15 hours or so, but be aware that there are no side quests and no real reason to replay once players reach the end.
Those who've tried the other recent Mario RPGs on the GameCube or Game Boy Advance and liked them will find this right up their alley.
Deaf and Hard of Hearing gamers will have no problems at all. All information is delivered through text or by non-verbal visual cues. I personally played this game almost entirely with the sound off, and encountered no issues or barriers whatsoever.