Parents and Bad Kids

Why can't some parents try a little harder to control their children's bad behavior in public places. There have been many times where my nerves have been rattled in a restaurant or some other public place because of some screaming kids who won't stop stop acting up. Whats worse is that many of these times their parents don't even try to take control of their kid's behavior, other than maybe telling them to stop it, which does not work, and sometimes they just let their kids run wild. Please parents, if your kid acts up in public, teach him or her to stop doing that.