Difficult topic. I can't answer the particular situation, but in general, I would probably ask myself the question of whether what I witnessed warranted genuine concern for a person's safety.
I called the police over the dog then the kids told me the rest this morning. I lived that way long long ago so I know it's just a matter of time before someone gets hurt. I don't involve myself with neighbors unless I see they have a need I can help with anonymously or if I see violence. They all know that I'm a no harm to kids or animals kind of person. If the mom asked for help I would but she's an adult and has a choice. The kids and dogs don't.