According to the ESRB, this game contains: Mild Cartoon Violence
The only thing parents have to worry about is excessive frustration. Kids will be pulling their hair out trying to get Billy to do what they want him to in some parts of the adventure because of the game's technical rough edges. Otherwise, everything is sunshiney cuteness. There are no sexual situations or any questionable language.
Platform game fans would be better off going with Jak And Daxter or Sly Cooper if they own a PlayStation 2. The technical production of Billy Hatcher is the pits, and feels like a last-gen game when compared to the PlayStation 2's heavy hitters. Otherwise, go for the Sonic Mega Collection on the GameCube for something with a more solid core.
Sonic Team fans will want to check out the game's extras. You can unlock a plethora of helper characters from other Sonic Team games like Sonic, NiGHTS, and Samba, as well as download a handful of small Game Boy Advance minigames.
Deaf and Hard of Hearing gamers will have no problems. All dialogue (and there's not much) is provided through text, and there are no significant auditory cues.