"In a classic study, Cialdini and colleagues manipulated the signs that were displayed in Arizona’s Petrified Forest National Park, a site often plagued by tourists who end up grabbing some of the petrified wood to take home as a souvenir. In situations like this, the first inclination of well-meaning environmentalists might be to set a strong prescriptive norm — perhaps by saying something like, 'Many past visitors have removed the petrified wood from the park, changing the state of the Petrified Forest. This is bad, don’t do this.' The idea here would be to invoke a sense of shame and severity before asking visitors to refrain from taking the wood. But read that prescriptive message once again. Is there anything descriptive in there? Yes, of course there is. That message is not just telling you that you shouldn’t take the wood — it’s also telling you that most other people do. In fact, people were actually more likely to steal wood from the forest when they saw the sign telling them how many people tend to do it themselves, even though the very next sentence was asking them to refrain. But when the researchers simply tweaked the message to read that 'the vast majority of past visitors have left the petrified wood in the park, helping to preserve the natural state of the Petrified Forest,' the thievery plummeted. [1]
Not a parent, but I would guess that kids are the same way only more so. The smart parent will make sure their kid sees other well-behaved kids most of the time.
[1] http://blogs.scientificamerican.com/psysociety/2013/03/28/ma...