During the course of the game, the dialogue contains some sexual references (e.g., “Now that was a sorry looking wh*re. Won't be selling her goods for a while,” “Your wife really enjoyed having a real man last night, shorty!” and “You going to try to feel me up again?”).
Sexual themes should be the least of a parents concerns with this game. I believe the blood and violence by far out ways the sexual themes.
The game is rated M for a reason. Sexual themes play a very small role in that rating.
ESRB ratings summary for "Assassin's Creed: Revelations":