Is it okay to parent someone else's kids when they are doing something wrong?

I can understand why parents don't like other people to correct their kids, even when they do something wrong in public. Because they know their children the best, they should be the ones to educate them and guide them in the right direction. That said, on many occasions, strangers feel the need to intervene. Some of them somehow feel like they could do a better job at parenting (probably not), and some of them just see no other choice in a particular situation. It very much seems like something you should never do, and it will be taken as an overstep in most scenarios. However, what if it was the right thing to do?

In this story, two women, who are also moms, are visiting a historical landmark in Boston. A cemetery that is a couple of centuries old. Because of its age, the tombs in the place are fragile and unstable. That's when they see a couple of children playing around, directly endangering the integrity of the historical artifacts. As their parents were not intervening, the two women decided to jump in and correct the kids as nicely as possible. When the parents saw this, however, they challenged the women's authority by telling the kids to disregard what they had been asked to stop doing. The parent's argument was that they were local kids, so they shouldn't be called out for playing in their own neighborhood.