There are many reasons that we leave adults in charge of children and we don't let a 5 year old kid be in charge of watching a bunch of younger kids. The main reason - kids make really dumb choices. What is the worst idea you had as a kid?
Facebook is a fantastic way to stay in touch with friends and acquaintances and let everybody know what you ate for lunch. It is also a great way to let the world know how good you look today or that you have completely forgotten everything taught to you in school.
Nobody want to be sued - so everyone nowadays is taking extra precautions to cover their rears! Some warning label are just ridiculous though...but it if keeps away the law suits, then I guess it is ok.