In an analysis of several studies, researchers found that children are more adept than previously known at understanding the subtleties of rules and social norms, in one instance insisting that puppets in a puppet show follow sets of behavior as they understood them from prior demonstrations.
However, the children in question seemed to understand that they could only be hard-asses with members of their own social group, and did not try to correct behavior of, say, those who speak a different language.
And, they know what these norms are without even being told — for the most part, the children studied seemed to have picked up behaviors simply by observing the adults around them in action, and acting (and judging) accordingly.
Excuse me while I make laminated copies of this study to hand out to every single parent who doesn't understand why their children should be expected not to run around in circles, screeching, waving, tormenting the public in crowded restaurants or, say, an 8 a.m. train. Also excuse me while I order a birth control refill.
The rest of you, keep walking on eggshells around these little terrors, they are picking up on your every move.