Does L.A. Noire have parental controls or a family / clean setting?
The game is categorized Level 9 regarding parental control. You can set the level you want on your PS3 to allow or avoid games of higher levels to be launched.
In-game, you cannot deactivate any explicit content (as for a lot of Rockstars games, there wouldn't be a lot still there...).
And as The Annoying Pyro says, always check covers for ESRB rating or other rating depending on location. Here (Europe), the game is rated 18, meaning you should not play before being 18. As James, I wait for my daughter to be in bed to play this kind of games.