Basically the less realistic or simpler you make something appear (gore, violence, hurt, weapons, humans, anything etc.) the "friendlier" it becomes ? for instance replacing all the bullets and characters in Call of Duty with cubes wouldn't appear violent to the masses even though all you're doing is changing the textures/mesh.
Another example: They made Tetris friendly to kids by using cubes, imagine if you replaced all the squares in Tetris with pieces of human flesh and when you fill up a line of flesh it ruptures and spills blood everywhere.