I can't say I've seen anything posted on the ranges I use, both indoor and outdoor. However, the one I'm a member of takes rudeness very seriously. Most of us are older and good manners are expected. The R.O.'s like to keep things running smoothly without and dissention. Besides, if the kids are crowding you, one must wonder how range savvy they are. Kids that are inexperience or untrained are a significant danger.
That being said, I like having well behaved kids at the range. The few younger folks that bring there kids have raised them right. And, as an old fart I really like the look on a kids face when mom or dad let's them try that "cool" gun the old man has over there. Kids are pretty smart, and when they see mom and dad shooting semi-auto handguns and someone shows up with a "cowboy" gun, they want to shoot it. Heck, that's what guns are for so I encourage them at every chance.