Hypothetical

I spent 10 years of my life in the law. Lawschool trained me to think through the use of "hypotheticals", a (sometimes) fictitious problem in need of resolution. (Unfortunately) I still think like that. Here is a hypothetical that I've been thinking a lot about lately:

A few years ago, Mrs. White met a neighbor, Mrs. Black, who lives down the street. They both have toddlers and exchanged phone numbers to arrange play dates. Neither mom contacted the other.

Over the next two years, Mrs. White rarely saw Mrs. Black. Recently, Mrs. White has been at the playground in the middle of the afternoon, at the same time as Mrs. Black's babysitter and Mrs. Black's two kids. Mrs. White observed that Mrs. Black's babysitter does not watch the kids, but rather is on her telephone and talking to other caregivers at the playground. Mrs. Black's kids continuely put themselves in dangerous situations and other caregivers need to step in to help them. Mrs. Black's kids also act as bullys, routinely throwing woodchips at other kids.

Question -- What do you do (which I think is obvious), but more importantly, how do you do it?