OMG Mature 17+ viedo games and Rated R Movies....

My son went to a friend's house last night and he came back telling me all these things the boys mother allowed him to do. Now my son't isn't even nine yet and he was allowed to Play left for dead 1 and 2 and watch Jaws and Aliens vs predetors which are all intended for adults NOT children. I dont' understand why adults don't monitor their kids to play this junk. Left for dead is nothing but violence. Killing, bashing and cutting up zombies, it's so full of blood and gore, and I do NOT allow my children to play or watch these types of games. What is wrong with people???????????????? GRRRRRRR.........