For anyone not familiar to this game, it was already given an AO rating. Rockstar was set to release it in early August when it received the AO and Nintendo and Sony refused to let it be released on their consoles. Rockstar then reworked the game to remove the most objectionable content until it was able to get the M rating. (Link
I have played this game on the Wii and it is definitely not for kids. Some of the killings actually made me squirm uncomfortably. However, the worst killings have been blurred out (a "rage-like" red fills the screen and everything gets noisy). Overall, it is what the rating says it is: a game for Mature adults... not for kids.