Oblivion is a game I own and enjoy, but it may be difficult for parents to decide whether it is kid-friendly. This is because of the sheer scope of the game. You can do almost anything. It is fully possible to charge through the streets, cutting down everyone in sight, although you will be pursued by guards and law enforcement agents if you do. Or you can be a perfectly righteous crusader for justice. The number of possibilities is nearly infinite. Some things that are constant are:
Violence. Usually, the violence in Oblivion is rather mild, no dismemberment or head-chopping, they just fall down, with small amounts of blood. However, there are some fairly disturbing things. When the player encounters zombies, they are VERY disturbing looking. They look like a human than has been fed through a wood-chipper, and then haphazardly put back together. They are stark naked (although partially skeletal, so no real nudity is shown) they do however, show lungs, intestines, and occasionally exposed brains. Similarly mutilated corpses can be found in the lairs of necromancers and other monsters. As for sex, there really is none, except the occasional mild innuendo. You have the choice, after killing a foe, to take all of their armor, leaving them only in underwear. No nudity. Language wise, it's seldom encountered, with the worst word being d***. I would recommend this game for tweens and up, if they can handle some of the more disgusting monsters.